« ZurückWeiter »
talite of Ytterby, although “a close examination" of several points in the history of the latter substance yet requires to be made, in order to establish the truth of such a conjecture.
New Haven, May 15, 1842.
On M. De Luc's Electric Column. By Thomas Forster, Esq. *
IN consequence of M. De Luc's Electric Columns having been described in your “ Philosophical Magazine,” I think it right to inform your readers of a circumstance relating to it which may prove interesting. I have observed that the action of this column is materially influenced by the state of the atmosphere : your readers are acquainted with the manner in which two bells, attached to the plus and minus end of the column, are made to ring by means of an insulating conducting clapper being suspended between them, and with the circumstance of their having rung for many months together in an instrument of Mr. B. M. Forster's, at Walthamstow. Now I have observed that they sometimes pulsate very strong and regularly, at other times weak and regularly, at others strong and irregularly, or with intervals of quiescence, and sometimes both weak and irregularly ; and these variations seem to me to be connected with peculiarities in the electric state of the atmosphere. For I cannot perceive that there is any correspondence between the kind of action of this column and the state of the hygrometer, barometer, or thermometer ; but there seems to be a connection between it and certain appearances of the clouds, the peculiarities of which are (according to the modern theory) caused chiefly by electricity : when the air is dry, with strong easterly winds, when the cirrus cloud ramifying about in all directions, and occasionally accompanied by the other modifications, continues for a long time unattended by rain; when the nights are clear, and small meteors, called falling stars, are numerous ; when I say these circumstances happen together, I have observed that the bells of this column always ring with very irregular pulsations; and further, when rain succeeds such kind of weather, it commonly happens that their pulsations become weak, or cease altogether, and the bells become silent: on the contrary, when the weather is fair, and when only diurnal cumuli prevail, they usually pulsate regularly. An ingenious meteorologist suggested to me the other day, that the irregular pulsation of the bells might be occasioned by the electric fluid's passing downward to the earth in pulsations, which might be the case when it was very irregularly distributed in the atmosphere.
To me it appears that this irregular distribution of the electric fluid would be indicated by the multiform appearance of the cirrus cloud which I have described, for the particular office of this cloud
• From " Tilloch's Philosophical Magazine.”
seems to be that of serving as a conductor of electricity. The same circumstance would also give rise to the occasional appearance of other modifications. All however that can be said on this interesting subject at present is, that there seems to be a connection worth attending to between the kind of action of the column, and the kind of weather which prevails, indicated by the various and peculiar appearances of the clouds. Future observations may lead to the knowledge of adjunct circumstances which may have their share in producing these changes. To engage the co-operation of other meteorologists, by which alone the science can be brought to any degree of perfection, is the object I have in view in soliciting the favour that this may be inserted in your “ Philosophical Magazine."
I remain, Sir,
THOMAS FORSTER. St. Helen's Place, June 14, 1811.
A Daguerreotype Experiment by Galvanic Light. By B. SILLIMAN,
Jun., A.M., of the departments of Chemistry and Mineralogy in Yale College, and Wm. Henry GOODE, M.D.*
In November, 1840, we succeeded in obtaining a photographic impression, by galvanic light reflected from the surface of a medallion to the iodized surface of a Daguerreotype plate. The large battery in the laboratory of Yale College, consisting of nine hundred pairs of plates, ten inches by four, was charged with a weak solution of sulphuric acid, and its poles adjusted with charcoal points, in the manner which is customary when an intense light is to be produced by means of this instrument. Two pictures were obtained, one of which is made up of a blur, or spot, produced by the light from the charcoal points, the image of the retort-stand, on which a medallion of white plaster rested, and the image of the medallion, but the lines on its face are not given. The camera was about six feet from the charcoal points when this impression was taken, and the medallion a little on one side, and in the rear of the points. The plate was exposed to the light about twenty seconds, and no means were employed either for condensing the light on the objects to be copied, or that reflected from them, on the lens which gave the image. The only lens employed was a French achromatic, three inches in diameter, and of about sixteen inches focal length. Another picture was taken of the medallion only, which was placed about two feet from the charcoal points, and the camera about four feet from it, and in such a position that the charcoal points did not come within the field of the lens. This picture, we regret to say, has been inadvertently destroyed. The plates used were of inferior quality, being some of the first of American manufacture.
* From the “ American Journal of Science and Arts."
These experiments were not published at the time they were made, because it was understood, that a gentleman distinguished for his scientific investigations was already engaged in studying this branch of the subject, with whose researches we had no wish to interfere, and the matter was abandoned mainly for this reason. Having been informed recently, however, that this gentleman had also abandoned it, we have concluded to give this account of our own experiments.
On the same occasion, an observation was made respecting the image given by the two charcoal points, when they were nearly in contact, and the battery in full operation, which we do not remember to have met with elsewhere. An image of each charcoal point is given, separate from that of the other, by a lens placed at a little distance. These two images differ remarkably in colour; one is of the colour of the flame afforded by the combustion of an alcoholic solution of strontia; the other resembles in colour the flame produced by the combustion of an alcoholic solution of chloride of sodium, more nearly than anything else with which we can compare it.
The charcoal points were shifted, each to the opposite pole of the battery, without producing any change in the colour of the light given off by the poles respectively. Other pieces of charcoal were substituted, in the place of those with which this phenomenon was first observed, but the difference in the colour of the two images was always present, and did not seem to be connected in any manner with the particular charcoal points employed, but the yellow image was uniformly given by one pole, and the purple image by the other pole of the battery. We are under the impression that the yellow coloured image was produced from the charcoal point in connection with the positive pole of the battery, and that the strontia coloured image came from the negative pole of the battery, though of this no note was made at the time. No attempt was made to ascertain by direct experiments whether these images possessed a different degree of power or not, in producing an impression upon an iodized plate. The difference in their colour was presumptive evidence that one image (that from the negative pole), possessed more of the chemical rays than the other. But evidence is (we are of opinion) afforded indirectly that such is the fact. The light from both charcoal points made a slight impression on the iodized plate before they were brought so close together as to unite in forming a general blur: these two small spots or impressions are nearly opposite, or at each extremity of one diameter of the blur, and without its circumference; one of them is more distinct than the other. Within the edge of the blur, and nearly in the same diameter with the two spots above named, there are also two impressions, darker and more strongly marked than is the general impression made by the light from the points. One of these spots is doubtless made by the light from one point, while the other is due to the light from the other point, and one of them far exceeds the other in distinctness. Now the more strongly marked spot without the blur, and the more
strongly marked one within it, are close to each other on the same edge of the blur, and are doubtless produced by the light from one and the same charcoal point. The two other spots, viz., that without and that within the blur, wbich are much less distinct, are close to each other at the opposite extremity of the diameter of the blur, and are also evidently produced by the light from the other charcoal point.
Yale College Laboratory, June 20, 1842.
Description of a Method of fitting up in a portable form the Electric
Column, lately invented by J. A. De Luc, Esq. Also an Account of several Experiments made with it. By B. M. FORSTER, Esq.*
Having been informed that a row of galvanic plates had been constructed without any fluid being interposed, and that it acted very sensibly on a gold-leaf electrometer, I formed one of about two hundred small circles of zinc, and the same number of blotting-paper and Dutch gold-leaf, the Dutch leaf being cemented on the paper with a solution of gum arabic; the blotting paper was double, iwo pieces were gummed or pasted together before the Dutch leaf was put on. Through these circles, or plates, a silken string was passed for connecting them together. This small instrument acted sufficiently powerfully on a very delicate gold-leaf electrometer to encourage me to make a row consisting of a greater number of' plates. To the two hundred I added about three hundred more, using, instead of the Dutch metal, silver-leaf, and inserted the whole in a glass tube fitted up with brass caps, screws, and balls. The instrument thus fitted up may be called an electric rod. I have some of these rods with the plates pot connected by a string through them; which, provided the glass tube is very nearly of the same diameter as the plates, may be the best way of placing them; but unless the tube fits accurately, the other mode will probably be found preferable, as the plates can be more easily placed regularly,
The Dutch metal, or silver-leaf, may either be fastened to the paper with gum, or paste made over the fire with flour and water.
The following experiments were made with a rod of five hundred series of plates ; whether with the one in which were two hundred plates of Dutch metal, or in which there were none, but silver-leaf instead, it is not necessary to mention.
21st Sept., 1809. One leaf of an electrometer made of Dutch metal kept fapping to and from the side of the glass many times, when connected with the electric rod.
- The ends of the rod being placed upon two electrometers, when the top of either of them was touched, the electrometer at the opposite end diverged more immediately.
• From Tilloch's “ Philosophical Magazine."
22nd Sept. The rod was placed at the bottom of an electrometer; one leaf was attracted to the side and flapped several times. This experiment shows that the electric power of these piles or columns acts through a portion of air: I held the upper part of the electrometer in my hand during this experiment.
24th Sept. A small piece of Dutch metal was attracted up to the ball at the zinc pole of the rod, and adhered to it.
4th Oct. A very light ivory needle, turning on a point (like a magnetic needle), was attracted by the rod; when a finger or a key was placed near one end of the needle, and the ball at the end of the rod also near the same end on the opposite side, the needle vibrated backwards and forwards. The needle was insulated, I believe, by a piece of amber.
- The needle, after having been touched by the silver-end pole, evidently receded from that pole; or, as it is commonly called, was repelled, having been charged with the same kind of electricity as that end of the rod possessed: the same effect was perceived when charged by the zinc pole.
- One leaf of an electrometer (Dutch leaf) moved, when one of the balls on the rod was placed over the top, without being in contact with it.
15th Oct. The ivory needle vibrated between the balls of two rods, one of which was at the zinc pole, the other at the opposite pole.
One column which I have made, consists of about five hundred plates, each about th of an inch in diameter. I have put at the zinc end a piece of cork cut like the head of a snake or eel, and at the other end another to resemble a tail. This column may be called an artificial electric eel (Gymnotus electricus): it is not inserted in a tube like the others, a silken string runs through the centre of the plates, which may be drawn tight; then wound round a pin which is in the mouth, or may be loosened if desirable. This eel acts powerfully on the electrometers. The power appears to me to vary much more than that of the columns in tubes : provided the outside of these tubes be dry, I do not know that the strength of their electric power changes.
18th Oct. Three rods, each of five hundred series, were supported upon insulated stands, and a plate of copper suspended at the silver pole of the combined apparatus; another plate was placed under this (as in the common electrical experiment of the dancing images), one very small piece (or more) of tissue-paper was attracted up and fell down, and a little image of the same paper reared up, and once remained suspended to the upper plate, but I could not make it dance up and down.
*22nd Oct. One ball or both ? of Cavallo's pocket electrometer diverged, when three rods were combined; the pith-balls are on wires. With these three rods I could not perceive the metallic taste in the mouth which is so perceptible even with a single piece of zinc and silver placed against the tongue. When the ball or balls ? of the electrometer moved, the opposite end of the apparatus was touched.