queen sees the light for the second time in her life. When swarming, bees are very loath to sting, and, according to Latter, should they do so the sting is comparatively 'innocuous.' An average swarm is about the size of a football and weighs about 4 lbs.

The hive which the swarm has left has for the time no queen, though potentialities of royalty exist in the numerous royal-cells. As soon as the first of these young queens is ready to emerge she bites through the cover of her cell, aided by some of the workers, and steps into the hive; but this does not take place until eight days have elapsed since the swarming. As soon as the young queen has been cleaned and has acquired a little strength and her wings have hardened, she begins to move about, and when she becomes aware of the other royal-cells with the pupae of her sisters therein she becomes violently excited, utters a well-known war-note, and attempts to tear open the cell of the oldest. Sometimes this is permitted, and the ruthless young monarch slays with her sting in turn the whole succession of royal infants. Should her strength fail her the slaughter is continued by the workers, who in any case greedily consume what royal-jelly is left in the cells, and draw the corpses of their victims out of the cells and cast them out of the hive.

This process of slaughter is, however, a very risky proceeding, for if anything should happen to the conquering and sole remaining queen on her wedding-flight, or at any other time, and if there were no larvae under three days of age (these can be reared into queens by a continuous diet of royal-jelly) the hive would become queenless, and a queenless hive rapidly falls into a state of death, damnation, and despair.' Therefore the bees usually guard the cells until the first queen has been fertilised and has returned to the hive, and also until it has been clearly settled that a second swarming is not to take place, for in that case the first hatched queen would lead the swarm and one of her sisters would be wanted to replace her in the hive. Should there be a second swarm it will centre round the young queen as yet unfertilised, and it may be that some of her sisters may then escape and join the swarm, in which case it either breaks up into as many small swarms as there are queens, or the queens fight till but one remains, or the workers put all to death save one. A fight between

two queens is a venomous and a deadly affair. Although sisters, although members of the same exalted and exiguous caste, they seem to be animated by the bitterest hatred, yet so strongly implanted in their being is their devotion to the future of the community that when, as they sometimes do, they get into a mutually murderous position where a stroke of the sting of each would kill the other, they immediately cease fighting and retire trembling for a time, apparently appalled at the prospect of the queenless hive which would result from their killing each other. After a time, however, the combat is renewed and one or other is slain.

Sometimes when a second queen enters the hive and the reigning queen is busy laying eggs, the presence of the intruder is concealed and a crowd of workers surrounds her on every side, balling' her in until she dies of hunger and suffocation, but they never sting her to death.

For the first few days (from two to six after her birth) the young queen shows no disposition to be married. Then a change occurs. She becomes restless, runs to the hivemouth and back, and presently makes a short experimental flight, for the first time seeing the sun and inflating to the full her breathing tubes. Soon she takes wider flights, always keeping her head directed to the hive. After a time she is followed by a group of drones, and as she towers into space one by one these suitors drop off until one, the strongest, remains to mate with her high up in the heavens. The act of mating is fatal to the male. It is thought that he dies of nerve-shock. Whatever the cause, most of his body falls dead to the earth, but he leaves part of it in the queen; this can only be removed when it has shrivelled up, and then, in some cases, only by the aid of the workers. The fertilised queen returns to the hive, having in her spermatheca no less than 200,000,000 spermatozoa, a supply equal to even her prodigious fecundity.

Once the queen is fertilised and has begun her ceaseless egg-laying the drones are more useless than ever. They have always been a nuisance in the hive, devouring the best honey, hustling the workers, impeding the work and fouling the combs; for, unlike the workers who can only rid themselves of undigested food when on the wing, the drones and the queen deposit their excreta in the hive for the workers to

clear away. Useless, and a great drain on the hive, they are yet suffered to survive a little while, but in a few days. that curious socialistic instinct that persistently impels the honey-bee to sacrifice the individual for the sake of the community-'l'esprit de la ruche' as Maeterlinck calls it-is awakened, and the workers unite to destroy the drones, either by driving them forth, or by forcing them into an empty comb and starving them to death, or by savagely attacking them with sting and jaws, till they are killed outright.

The same 'esprit de la ruche,' the same overwhelming instinct to provide at all costs for the continuance of the race, causes the worker-bees to work themselves to death in a few weeks for the sake of succeeding generations, and condemns the queen-bee to a life sentence, which often takes four or five years to work out, of penal servitude in pitchy darkness.

A. E. SHIPLEY.

THE PRODUCTION OF POWER

1. Die Dampfturbinen. By A. STODOLA. Berlin: Julius Springer. 1910.

2. The Design and Construction of Internal Combustion Engines. By HUGO GÜLDNER. Constable. 1910.

3. Diesel Engines for Land and Marine Work. By A. P. CHALKLEY. Constable. 1913.

4. Power House Design. By J. F. C. SNELL. Longmans, Green. 1911.

5. The Gas, Oil and Petrol Engine. By D. CLERK and G. A. BURLS. Longmans, Green. 1913.

THE

HE rapid progress made in the production of power during the two last decades started when the industrial development of electricity made it possible to transmit power to a distance, and brought into existence the new industry of producing power for sale. Twenty years ago there were only a few insignificant or experimental electrictransmission plants; neglecting these, power could be transmitted over a distance exceeding a few tens of yards by three methods only by ropes, by compressed or rarefied air in pipes, and by water under pressure in pipes. Transmission of power by ropes was common on the Continent, but its distribution was impracticable. Power was, and still is, distributed by water in London, but the only non-electrical transmission and distribution plant that ever operated on a large scale was the compressed-air system in Paris. Twenty years ago power was distributed for sale only by a few isolated plants. Now, in England alone there are 350 electric stations distributing a total of some 1,000,000 horse-power for producing light, heat, or mechanical power.

The progress in power generation must be regarded as a direct consequence of the development of the business of selling power, because this business for the first time gave to engineers both the incentive and the means to study and ascertain the cost of producing power. The incentive lay in the natural desire for the success of the business, which,

apart from the minor costs of distribution, depends entirely on the cost of production. The means lay in the ease of measuring electrical power and of ascertaining every item making up the total cost of each unit generated. Armed with this knowledge, and with a knowledge of his colleague's work, an engineer can at once lay his finger on any point where undue waste occurs, can compare the economy of his different engines, and can from published data compare the running of his station with that of another station equipped with different plant. The effect of these facilities is seen with striking clearness on comparing plants installed in power-distributing stations with private plants in factories. While many of the latter are thoroughly up to date, there are still an enormous number of factories which have retained machines and methods, good in their day, but now so bad, as compared with modern standards, that the saving in a few years' working of a new plant would pay its initial cost. That such cases can exist in the light of present knowledge is due, first, to the factory manager not having the same interest as the station engineer in reducing his power costs, because they often form but a small item in the total costs; secondly, to his not knowing what the power costs are in relation to the power generated, because he either does not or cannot carry out the work of measuring the power; and thirdly, to his not having the expert knowledge needed to determine what is the best power plant for the particular conditions. of the factory.

This last is the main difficulty; there is no such thing as a best type of power plant, though a particular type of plant is generally the best for a particular set of conditions. The cost of power production depends more on the conditions of supply than on the plant itself, and of all the conditions affecting the cost, the most important is the 'load factor.' This factor is defined in more than one way, but is generally taken to be the amount of energy actually generated in the year expressed as a percentage of the amount which would be generated if the plant worked at full load night and day. Chemical factories often require a continuous and steady load, and their load factor then approaches 100 per cent. The ordinary factory, working day-time only, has a load factor of from 20 to 30 per cent. Electric light stations have the