114 



NATURE 



[Nov. 29, 1883 



them to contract as the speed increased. The governor mea- 

 sured by contraction the velocity of the engine, «hile the ther- 

 mometer measured by expansion the velocity in the particles of 

 matter which surrounded it ; so that it could now be seen that 

 having to perform two operation , the one on a visible scale, the 

 other on a molecular scale, the same class of mechanism had 

 been unconsciously adopted in perfornnng both operations. 



The purpose for which these Kinetic engines was put forward 

 was not that they might be expected to simplify the theory of 

 thermodynamics, but that they might show what was being diiue. 

 The theory of thtrmodynamics could 1 e dtduced by the laws of 

 motion from any one of these Kinetic engines, just as Rankine 

 deduced it from the hy| olheses of molecular vortices. 



Nothing had yet been said of the third part which heat played 

 in performing woik, narely, Ci-nveying heat in and out of 

 matter. It was an innovation to introduce such consideratii us 

 into the subject of thermodynamics, but it properly had a place 

 in the theory of heat-engines. It was on this part that the s, eed 

 at which an engine would perform work depended. 



The kinelic naehim-s showed this. If one end of a chain was 

 shaken, the wriggle ran along with a definite speed, so that a 

 definite interval must elapse before sufficient agitation was 

 established to raise the bucket ; further, an interval must elapse 

 before the agitation could be withdrawn, so that the bucket 

 might be lov\ered for another strole. The kinetic machine, 

 with the pump, could only work at a given rate. He could 

 increase this rate by shaking harder, but then he expended more 

 energy in proportion to the work done. This exactly corre- 

 sponded with what went on in the steam-engine, only owing to 

 the use of separate vesseb', the boiler, c) Under, and condensers, 

 the connection was much confused. But it was clear that for 

 every h.p. (2,ooo,oco ft. -lbs. per hour) 15,000,000 ft. lbs. had 

 to be passed from the furnace into the boiler, as out of the 

 I5,ooo,coo no more than 2,ooo,oco could be used for work ; the 

 remaining 13,000,000 were available for forcing the heat into 

 the bi iler and out of the steam in the condenser, and they were 

 usefully employed for this purpose. 



The boilers were made as small as sufficed to produce steam, 

 and this size was determined by the difiference of the internal 

 temperatures of the gases in the furnaces, and the water in the 

 boiler ; and whatever diminished this difference would neces-arily 

 increase the size of the heating surface required, i.e. the weight 

 of the engine. The power which this diffeience of temperature 

 represented could not be used in the steam-engine, so it was 

 usefully employed in diminishing the size of the engine. 



Most of this power, which in the steam-engine was at lea>t 

 eight times the power u«ed, was spent in getting the heat from 

 the gases into the metal plates, for gas acted the part of con- 

 veyance far less readily than boiling water or condensing steam. 

 If air had to be heated inside the boiler and cooled in the 

 condenser with the same difference of temperature, there would 

 be required thirty or forty lin es the heating surface — a conclu- 

 sion vhich sulficiently explained why attempts to substitute 

 hot air for steam had failed. In one respect the hot-air engines 

 had an advantage over the steam-engine. During the operation 

 in the cylinder the heat was wanted to be kept in the acting 

 substance ; this was easy with air, for it was such a bad con- 

 ductor of heat, that unless it was in a violent stJte of internal 

 agitation it would lose heat but slowly, although at a tempera- 

 ture of loco degrees and the cyhnder cold. 



Steam, on the other hand, condensed so readily that the 

 temperature of the cylinder must be kept above that of the 

 steam. It was this fact which limited the temperature at which 

 steam could be used. Thus, while hot air failed on account of 

 time economy, the practical limit of the economy of steam was 

 fixed by the temperalure which a cylinder would bear. These 

 facts were mentioned because at the present time there appeared 

 to be the dawn of substituting combustion-engines in place of 

 steam engines. 



Combustion-engines, in the shape of guns, were the oldest forai 

 of steam-engine. In these, the time required for heating the 

 expansive agent was zero, while they had the advantage of 

 incondensible gas in the cylinder, so that if ihe cylinder was 

 ■kept cool it cooled the gas but slightly, although this was some 

 3000 degrees in temperature. 



T he disadvantage of these engines was that the hot gas was 

 not sufficiently cooled by expansion, but a considerable amount 

 of the heat carried away might be used again could it be 

 extracted and put into the fre-h charj^e ; to do this however, 

 would introduce the difficulty of heating-surface in an aggravated 



form. However, supposing the cannon to have been tamed and 

 coal and oxygen from the fir 10 1 e u-ed instead of gunpowder. 

 T heimodynamic; showed that such engines should still have a 

 wide margin of economy over steam-engines, besides the advan- 

 tage of working with a cold cylinder and at an unlimited speed. 

 The present achievement of the gas-enfine, stated to be some 

 2,GOO,coo ft. -lbs. per lb. of coke, looked very promising, and it 

 was thus not unimportant to notice that whatever the art 

 difficulties might be, thermodynamics showed no barrier to 

 further economy in this direction, such as that which appeared 

 not far ahead of what was already accomplished with steam- 

 engines. 



But however this might be, he protested against the view 

 which seeirerl som.ewhat largely held that the steam-engine was 

 only a semi-barbarous machine, which w.asted ten times as much 

 heat as is used — very well for those who knew no science, but only 

 waiting until those better educated had lime to turn their attention 

 to practical matters, ai.d then to give place to sumething better. 

 Thermodynamics showed the perfections not the faults of the 

 steam-engine, in which all the heat was used, and could only 

 enhance the admiration in which the work of those must be 

 held who gave, not only the steam-engine, but the embodiment 

 of the silence of heat. 



PROFESSOR AUGUST WEISMANN ON THE 

 SEXUAL CELLS OF THE HYDROMEDUS^"- 

 pROF. WEISMANN of Freiburg is most highly skilled and 

 -*• most indefaligable in research, and all the memoirs which 

 he publishes are or extreme scientific importance, and abound 

 in original views and suggestions which render them of peculiar 

 and widely spread interest. His " Studien zur Descendenz 

 Theorie," his researches on the Daphnoids and on the fauna of 

 I ake Constance, w hich .are known to all naturalists, may be 

 mentioned as examples of his work. Since the spring of 1878 

 till the present year he has been engaged in investigating the 

 mode of origin of the gi.nad elements of the Hydromedusa;, and 

 the result- are embodied in the present splendid work, which 

 consists of a volume of text of about 300 pages quarto and 

 twenty-four most beautifully executed coloured plates, the whole 

 representing a va t amount of laborious research. Some portions 

 of the results have already api eared in short preliminaiy papers, 

 but they form a very small in talment of what is here put forth. 

 In the course of the investigation, which has extended to thirty- 

 eight species of Hydromedusa;, important new observations on 

 the habits and composition of Hydroid colonies generally and 

 on their histology were made, and the results of these are fully de- 

 scribed here, since most of them have a direct bearing on the 

 elucidation of the main subject of the monograph. The work 

 thus forms secmdarily, as stated in the tiile-page, " a contribu- 

 tion to the knowledge of the structure and vital phenomena of 

 the Ilydromedusoe generally." 



The principal value of the work, however, lies in the import- 

 ance of the bearings of the results of the investigations detailed 

 in it upon the general question of the origin of gonad cells. 

 The HydromedusK: were selected as the subject of research 

 btcau-e they appeared to be of all groups of the animal kingdom 

 be-t adapted tor the purpose both becau-e of the transparent 

 nature of the r tis ues and becau-e they present in closely allied 

 fo: ms so many remarkable differences in the development of the 

 gonad elements. 



The work commences wiih an historical introduction, which 

 can be but briefly referred to here. The que- tion of the origiii ot 

 the sexual elements in the Hydroida has undergone several im- 

 portant transformation*. Prof. Huxley, when he first defined 

 the body of the Medusa as consisting of two layers of tissue — 

 ectoderm and cndoderm, raied the question in which of the 

 two layers do the gonad elements originate, and at first concluded 

 that they were formed between the two, and subsequently in 

 1859, from physiological considerations mainly, that they must 

 originate in the ectoderm. As soon as the advance of histological 

 method permitted accurate direct observation to be made on the 

 matter, Kefer.-tein and Eblers showed that in the Siphonophora 

 with well developed medusoid sfxual individuals, the Calyco- 

 phorida; andma'e Physophorida;, the germinal cells are developed 

 in w hat is now recoj^nised as the ectoderm of the manubrium ; 

 ■ •■Die Entslehung der Sexualzellen bei den HydromeJu'en." Zugleich 

 ein Beitrag lur Kenntniss des Baues und der LeLenserscheinungen dieser 

 Gnippe, von Dr. August Weismann, Professor in Freiburg-i Br. (Jena: 

 G. Fischer, 1E83.) 



