height as to be completely full, when the standard piece S, and the bulb of thermometer t are immersed.

B is a cylindrical vessel of tinned iron, 14 inches high, and 9 inches in diameter, to which is adapted the cover D of the same material, having in the middle a circular aperture a a, 3 inches in diameter, for receiving the thermometer t, and the standard piece S; allowing likewise sufficient space to move the suspending wire and thermometer. Another aperture through D, near

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its circumference, admits the lower part of the thermometer i, and an opening near the bottom of B, receives the bulb of the thermometer l.

The thermometer O was suspended just without the vessel B, to mark the temperature of the room. C is a support for the water vessel A, formed of a cylindrical block of charcoal, 4 inches high.

The method of adjusting the weight of water in A, in this series of experiments, was the same as that subsequently described

tial temperature about 62°, it has not been deemed necessary to make more than one correction for the quantity of mercury expelled from the bulb, or excluded from the influence of the water vessel. At 62° the bulb must have held, by calculation,* 4670 grains of mercury, which, by a mean of several determinations already published, possesses a specific heat of .0327, and gives an equivalent, in grains of water, of 152.7.

When this thermometer was used in connection with a containing vessel of glass, the weight of its bulb was added to that of the vessel; and in other cases, the specific heat attributed to it, was that obtained by means of several trials of it with glasses of different thicknesses, instituted with a view to determine the effect of that material, towards cooling the heated body or standard piece. The specific heat thus found, was .10036, according to which the bulb would be equivalent to 43.45 grains of water. The length of the scale of this thermometer was 37 inches, and the graduation extended from 34° to 74°; so that each degree was nearly 37 of an inch in length, and the degrees were divided each into 50 parts, each part being of such magnitude that the eye could, when necessary, easily subdivide and read them into hundredths.

The graduation of this thermometer was obtained by direct comparison with a welltried standard instrument, the degrees of which were about one-quarter of an inch in length. For this purpose, the bulbs of both were immersed in a large quantity of water, contained in a Hessian crucible, surrounded by another of black lead; thus affording a combined mass which changed its temperature with extreme slowness, and enabled us to mark, with deliberation and accuracy, every degree on the long scale, after having for some time agitated the two in contact with each other, and tempered the water to the point required.

The general mode of operating with the apparatus, Plate VII., was, after giving the water vessel and thermometer t, a temperature a few degrees below that of the surrounding air, to take simultaneous observations of all the thermometers which were recorded by one assistant, while another person, bringing the hot standard piece, sur

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rounded by its shield, from a distance of about 4 feet out of the heating apparatus (Plate VII), immersed and held it suspended, as already described. The moment of immersion was observed by a second assistant, on a time-keeper marking seconds. The manipulator, continually moving the thermometer t, and the standard piece about in the water, read off the degrees and parts as successively attained by the mercury, while the second assistant noted, and the first recorded them, together with the time of each observation.

The method just described, afforded the means of determining approximately, the proper temperature below that of the air, at which the water ought to be, when the standard-piece was immersed, in order that the heating and the cooling power of the atmosphere should be equal to each other. Table XIV will be found to contain a synopsis of the experiments conducted in this manner with reference to different containing vessels. Some trials were made to ascertain, with different vessels, the rate at which the air alone would, under given circumstances, produce certain elevations or depressions of temperature. But the interference of extraneous causes, such as the presence or absence of a stove in the apartment, the heat derived from the person of the observer, and others near the scene of the experiment, made it evident that a good defence against the influence of the air would be a better guarantee against error, from that source, than any table of corrections which could be constructed amidst so many modifying causes.

The results of a series of trials made in part without employing the vessel B to defend the water from the air and from radiation, are exhibited in Table IV. Some attempts were made, as above referred to, towards the correction of the irregularities therein observed; but the uncertainty attending the process, induced the committee to prefer, when practicable, the prevention to the correction of these anomalies. As the vessel B held 924 cubic inches, the whole quantity of air it could contain did not exceed 277 grains; which, supposing the specific heat of air to be .26, would not be equivalent to more than 72 grains of water, but as a considerable portion, amounting to at least of the whole, was occupied by the water vessel and its support, the remaining air could in no instance have been equivalent to more than 62 grains of water, and as the greatest change which occurred in the temperature of this portion of air during any experiment, was but 1.7°, and as the mean of all the changes of this kind observed during the progress of the investiga

tion, was a grain of 0.325°, while the correspondent mean gain of temperature in the water was 7.26°, and the mean weight of the latter 13.100 grains, it is evident that the relative influence of the air and of the water will be represented by 62 grains × 0.325° = 20.15 and 13100 grains x 7.26° = 95106, or the former is part of the latter, from which it appears that from this cause the expression for the specific heat could not have been affected under the fifth place of decimals.

In a series of 13 trials in which the water, amounting to about 40,000 grains, was contained in copper vessels (Table VIII.), and the rise of temperature in the same was at a mean about 2.5° the air gained about .292 of a degree, which would indicate that the cooling power of the air confined in the vessel B, compared with that of the water in A was but as 1 to 5550, a result which would still less affect the general correctness of the determination.

[The limits to which the size of our Magazine confines us, prevents our republishing the elaborate tables of experiments, now and hereafter referred to, which would of themselves occupy a goodly octavo volume. The results of these experiments here stated, will, however, we have no doubt, be sufficient to satisfy a great majority of our readers. We refer those who desire to enter more deeply into the subject and to attain a more intimate knowledge of the experiments (we should particularly recommend them to the attention of Mr. Parkes and Captain Pringle, the engineers appointed by the British government to investigate the subject of Steam Boiler Explosions; also to some of our respected cerrespondents, among others, Mr. Tomlinson, Mr. Wigney, and Dr. Schafhaeutl) to the Journal of the Franklin Institute, from which we extract these reports, vol. xix, pp. 94 to 105, for tables IV. to IX; the pages of the Journal where the subsequent tables are to be found, we shall point out in their proper places as they occur in the report.]

After the preliminary series already given (Table IV.), two other sets of experiments were made, one in each of two glass vessels similar to that in which the preceding trials had taken place,-equal to each other in liquid capacity, but of different thicknesses; the one being more than four times as heavy as the other. Table V. contains the experiments with the thicker, and table VI. those with the thinner of these vessels. The particular object of these trials was to

determine, if possible, the effect of the containing vessel on the general result of the experiment; in other words, to decide its specific heat, by observing the difference which would arise from a mere change of thickness in the containing vessel, while all other circumstances of the trial were the same in both cases. A comparison of several experiments in each table, with corresponding ones in the other, will show that when the water at the commencement was from 60° to 63.5°, the actual difference in the rise of temperature, due to a difference in the weight of the containing vessels of (12272-2996)=9276 grains of glass, was about three-tenths of a degree; and from the comparison of nine experiments in the first of these tables, with the same number in the second, it will be seen that we obtain for the specific heat of glass .111063*. A part of the trials in these and the subsequent series were made by means of the spirit thermometer C, the equivalent of which was only approximately found, on account of not having taken the precaution to weigh the bulb and tube separately before filling the instrument. It is also, like all other spirit thermometers, liable to some uncertainty in its indications owing to the different quantities of the liquid which may at different times be taken up in wetting the tube, an uncertainty, which is the greater, the more sudden are the changes to which we submit the instrument.

The equivalent value assigned to it by finding the weight and capacity of an equal length of the same tube is 117.4 grains of water, as hereafter mentioned.

The next apparatus used in this part of the investigation consisted of two glass jars, smaller than those above described, both of the same capacity, but differing from each

To'g-T' tg'

of the container; T" is the gain of temperature by the water when the thinner glass is used; T the gain when the thicker vessel is employed; t', is the loss of temperature by the iron when the thinner, and t, that when the thicker is employed; w, is the weight of water in both cases, and e the equivalent in grains of water, of the liquid in the thermometer; g is the weight of the thicker jar; g' that of the thinner. Thus comparing the two identical experiments 7 and 8, table V., with experiment 6, table VI., in which the initial temperature of the water, and other circumstances, coincided with the former, we have 7" 5 deg. 76; t = 143 deg. 1; T= 5 deg..4; 142 deg. .74; w= 16494.5 grs. ; e=152.7 grs.; g = 12.706 grs., and g' 34.30 grs. Hence T824.256; T= 770.796; Tt-Te 54.46; we 16-647.2; Tt'g: 9793733.976; -2827198.08; from which .130156 the specific heat of the glass by this comparison.

=

other in weight, being nearly in the proportion of 3 to 1. The experiments in

these two vessels were made in two sets of 6 each, three of each set being commenced in the thicker vessels, at a temperature of 60°, and three at 60.5°; and the same number at the same two points in the thinner. The results are contained in table VII., where it will be perceived that, from five comparisons between the trials in these two jars, the influence of the glass is such as to indicate a mean specific heat of .103086, which taken with the above result of the nine comparisons, between Tables V. and VI. gives a mean specific heat of flint glass of .107074.

As we are now only referring to the apparatus employed, we shall reserve our remarks on the results presented by these tables, respecting the specific heat of iron, until we have described the other methods of verifying their correctness.

The fourth set of apparatus for this purpose, consisted of two cylindrical copper vessels, of the same height as the glass ones already described: but of such diameter as to contain about 38600 grains, or a little over 5 pounds avoirdupoise of water, and so differing in thickness, that the one weighed nearly four times as much as the other. The mode of conducting experiments in these two vessels, and the principle of calculation applicable to them, is entirely similar to that already given for the two pairs of glass jars,-except that the equivalent of the glass in the thermometer, was now separately computed.

The results will be found in table VIII., in which it will be perceived that the number of comparisons furnishing data for determining the specific heat of copper, is but two, and of these only one can be considered entirely unexceptionable.

From this it should seem that the specific heat of copper is .10431, whereas the four dsterminations of Wilkie, Crawford, Dalton and Petit and Dulong give .10750 for the specific heat of that metal.

A fifth mode of determining the specific heat of iron was by employing as water vessels two cylindrical sheet iron jars of the same capacity, but of thicknesses differing from each other in about the proportion of 3 to 1. As in the preceding sets, the specific heat of the container may here be found by comparing together experiments made at the same temperature, in the two vessels; and this ought to give their variation, if any exist, from the specific heat of the standard piece itself. Another method is to assume that the specific heat of the standard piece and of the sheet iron con

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tainers is the same.* The use of the two containers in this latter case serves only to verify each others results, since each furnishes a separate and independent calculation.

The results of experiments in the two iron vessels will be found in Table IX. A comparison furnished by two experiments in each vessel, gives by calculation on the principle used in the case of the glass containers the specific heat of the Russian sheet iron, of which they are composed = .101714.

Results of Experiments on Specific Heats. -When it is considered that numerous causes interfere with the operations on specific heats, it cannot be expected that one, or a few trials, should be deemed sufficient to settle so difficult and intricate a question. For this reason the committee preferred the method of multiplying and varying the trials, and making a deduction from the mean results, in order to verify the general efficacy of the standard piece, in producing vapour.

1. The first part of the preliminary series (table IV.) indicates the effect of radiation from surrounding objects in the apartment to the water-vessel. The 13 experiments constituting this part of the table, exhibit a mean result of .123004 as the specific heat of iron.

2. The second part of the same series in which the cylinder B. was employed, indicates a decided effect from that precaution, and gives as a mean result .11294, for the specific heat.

3. Experiments No. 16, 20, 23, 25 and 26, the greatest number of comparable results in this part of the series, (differing only in the fourth place of decimals,) gives a mean of .11346.

4. In table V., where the thicker of the two glass cylinders of the same capacity was used, we have the mean result of the whole 14 experiments .11288.

5. The four experiments No. 2, 5, 6, and 9, which are the greatest number that conform to the third place, give a mean result of .11349.

6. The 10 experiments in table VI., made in the thin cylinder of the same capacity as the foregoing, give the specific heat = .11308.