June 8, 1876] 



NATURE 



141 



occupation, an occupation that places them on a level with the 

 turnspit. It is one which is most properly meted out in our 

 prisons as a punishment for crime, accompanied, however, with 

 the degradation that the force exerted shall be entirely wasted in 

 idly turning a fan in the free air, and thus the prisoner, in addi- 

 tion to the fatigue of his body, undergoes the humiliation of, as 

 he expresses it, " grinding the wind." 



If they played no other part than that of relieving humanity 

 from such tasks as these, prime movers would be machines to 

 be hailed. 



Tiue it is that the labourers who were thus relieved would not 

 thank their benefactors, and indeed so far as the individuals 

 subjected to the change were concerned they would have 

 cause not to thank them, because tbey having been taught no 

 other mode of earning a livelihood, and finding the mode they 

 knew set on one side by the employment of a prime mover, 

 would be at their wit's end for a means of subsistence, and 

 would be experiencing those miseries which are caused by a state 

 of transition. But in some way the men of the transition state 

 must be relieved, and in the next generation, it no longer being 

 possible to subsist by such wholly unintelligent labour, the 

 energies of their descendants would be devoted to gaining a 

 livelihood by some occupation more worthy of the mind of 

 man. 



Early prime rroveri', from their comparatively small size, 

 probably did little more than thus relieve humanity ; but when 

 we come to consider the prime movers of the present day, by 

 which we are enabled to contain within a single vessel and to 

 apply to its propulsion 8,coo indicated horse-power, or an equi- 

 valent of the labour of nearly 50,C!00 men working at one time, 

 we find that the prime mover has another and most important 

 claim upon our interest : it enables us to attain results that it 

 would be absolutely impossible to attain by any aggregation 

 of human or ether muscular effort-, however brutally indifferent 

 we might be to the misery of those who were engaged in that 

 effort 



Excluding from our consideration li^ht and even electricity, as 

 not being, up to the present time, sources of power on which we 

 rely in practice, there remain three principal groups into which our 

 prime movers may be arranged, viz., those which work by the 

 agency of wind, those which work by the agency of water, and 

 those which work by the agency of heat. But some of these 

 great groups are capable of division, and indeed demand division 

 into various branches. 



Water power may be due to the impact of water, as in some 

 kinds of water-wheels, turbines, and hydraulic rams, or to water 

 acting as a weight or pressure, as in other kinds of water-wheels, 

 and in water-pressure engines ; or to streams of water inducing 

 currents, as in the case of the jet -pump, and of the "Trombe 

 d'eau," or to its undulating movements, as in ocean waves. 

 The ability of water to give out motive force may arise from 

 falls, from the currents of rivers, from the tides, or, as has been 

 said, from the oscillation of the waves. 



Prime movers which utilise the force of the wind are few in 

 number and in all cases act by impact. 



As regards those prime movers which work by the aid of heat, 

 we may have that heat developed by the! combustion of fuel, 

 and being so developed applied to heating water, raising steam, 

 and working some of the numerous forms of steam-engines ; or, 

 as in the case of the Giffard injector, performing work by in- 

 duced currents, by the flow of steam ; or we may have the heat 

 of fuel applied to vary the density of the air, and thus to obtain 

 motion as by the smoke-jack ; or the fuel may be employed to 

 augment the bulk and the pressure of gases, as in the numerous 

 caloric engines ; or we may have heat and power developed in 

 the combustion of gases, as in the forms of gas-engines ; or in 

 the combustion of explosives, as in gunpowder, dynamite, and 

 other like materials, used not only for the purposes •f artillery 

 and of blasting, but for actuating prime movers in the ordinary 

 sf nse of the word. 



Again, we may have the heat of the sun applied through the 

 agency of the expansion of gases or surfaces to the production 

 of power, as in the sun-pumps of vSolcmon de Caus and of 

 Belidor, and as in the sun-engine of Eiricsson. Finally, we may 

 have the sun's rajs applied direct, as in the radiometer of Mr. 

 Crookes. 



A consideration of the foregoing heads, under which prime 

 movers range themselves, will speedily bring us to the conclusion 

 that the main centre of all mechanical force on this earth is the 

 sun. If the prime movers be urged by water, that water has 

 attained the elevation from which it falls, and thus gives out 



power by reason of its having been evaporated and raised by the 

 heat of the sun. If the power of the water be derived from 

 the tidal influence, that influence is due to the joint action of the 

 sun and the moon. 



If the prime mover depend upon the wind for its force either 

 directly, as in windmills, or indirectly, as in macliines worked by 

 the waves, then that wind is caused to blow by variations of 

 temperature due to the action of the sun. If the prime mover 

 depend upon light or upon solar heat, as in the case of the 

 radiometer and of the sun engine, then the connection is 

 obvious ; but if the heat be due to combustion, then the fuel 

 which supports that combustion is, after all, but the sun's rays 

 stored up. 11 the fuel be, as is now sometimes the case, straw or 

 cotton stalks, one feels that they have been the growth of the 

 one season's effect of the sun's rays. If the fuel be wood, it is 

 equally true that the wood is the growth of a few seasons' exer- 

 cise of the sun's rays, but if it be the more potent and more 

 general fuel coal, then, although the fact is not an obvious one, 

 we know that coal also is merely the stored up result of many 

 ages exercise of solar power. 



And even in the case of electrical prime movers, these de- 

 pend on the slow oxidation, that is burning, of metal which has 

 been brought into the metallic or unburnt state from the burnt 

 condition (or that of ore) by the aid of heat generated by the 

 combustion of fuel. 



The interesting lecture-room experiment with glass tubes 

 charged with sulphide of calcium, or other analogous sulphides, 

 makes visible to us the fact that the sun's rays may be stored up 

 as light ; tut that they are as truly stored up (although not in 

 in the form of light) in the herb, the tree, and the coal we also 

 now know ; and we appreciate the far-seeing mind of George 

 Stephenson who astonished his friend by announcing that a 

 passing train was being driven by the sun. We know that 

 Stephenson was right, and that the satirical Swift was wrong when 

 he irstanced as a type of folly the people of Laputa engaged in 

 extracting sunbeams from cucumbers. The sunbeams were as 

 surely in the cucumbers as they are in the sulphide of calcium 

 tubes, but in the latter case they can be seen by the bodily 

 eye, while in the foraer they demand the mind's eye of a 

 Stephenson. 



Athough the sailing of ships and the winnowing of grain 

 must from very early time have made it clear that the wind was 

 capable of exercising a moving force, nevertheless, being an in- 

 visible agent, it is not one hkely to strike the mind as being fit to 

 give effect to a prime mover, and therefore it is not to be won- 

 dered at that prime movers actuated by water are those of which 

 we first have any record, imless indeed the toy steam-engine of 

 Hiero may be looked upon as a prime move anterior to those 

 urged by water. It would appear that in the reign of Augustus 

 water-wheels were weil known, for Vitruvius, writing at that 

 time, speaks of them as common implements, but not so 

 common as to have replaced the human turnspit, as we gather 

 from his writirgs that the employment of men within a tread- 

 wheel was still the most ordinary mode of obtaining a rotary 

 force. It wou'd seem, however, that water-wheels driven by 

 the impact of the stream upon pallet boards were employed in 

 the time of Augustus not merely to raise water by buckets placed 

 about the circumference of the wheels, but also to drive mill- 

 stones for grinding wheat, ard Strabo states that a mill of this 

 kind was in use at the palace of the King of Pontus. 



{To be continued.) 



SCIENTIFIC SERIALS 



Poggendorff^ s Annalen der Phynkund Chemie, No. 2, 1876. 

 — In the opening paper of this number Dr. Konig describes a 

 series of researches in which he sought to study more closely the 

 phenomena which occur when two sets of sound-waves meet in 

 air ; using sources of sound that were entirely isolated and 

 could not act directly on each other, nor in common en a third 

 body ; he also chose sources that would give as simple tones as 

 possible. The paper is in four parts, treating, severally, of pri- 

 mary beats and beat- tones, secondary beats and beat-tones, 

 diffeT?nce-tones and summation tones, and the nature of beats 

 and their action, compared with the action of primary impulses. 

 On the last head he finds, inter alia, that beat-tones cannot be 

 explained by the cause of difference and summation tones, and that 

 the audibility of beats depends only on the number and intensity 

 of the primary tones, not at all on the width of the interval. The 

 number of beiats and primary impulses with which both may be 



