April %, 1 8 75 J 



NA TURE 



455 



very important, but have not hitherto received much 

 attention. A chemical transformation is impossible, if its 

 occurrence would involve the opposite of dissipation (for 

 which there is no convenient word) ; but it is not true, 

 on the other hand, that a transformation which would 

 involve dissipation must necessarily take place. Other- 

 wise, the existence of explosives like gunpowder would be 

 impossible. It is often stated that the development of 

 heat is the criterion of the possibility of a proposed trans- 

 formation, though exceptions to this rule are extremely 

 well known. It is sufficient to mention the solution of a 

 salt in water. This operation involves dissipation, or it 

 would not occur, and it is not difficult to see how work 

 might have been obtained in the process. The water may 

 be placed under a piston in a cylinder maintained at a 

 rigorously constant temperature, and the piston slowly 

 raised until all the water is evaporated, and its tension 

 reduced to the point at which the salt would begin to 

 absorb it at the temperature in question. After the salt 

 and vapour are in contact, the piston is made to descend 

 until the solution is effected. In this process work is 

 gained, since the pressure under the piston during the 

 expansion is greater than at the corresponding stage of 

 the contraction. If the salt is dissolved in the ordinary 

 way energy is dissipated, an opportunity of doing work 

 at the expense of low temperature heat has been missed 

 and will not return. 



The difficulty in applying therm odyn ami cal principles 

 to chemistry arises from the fact that chemical transfor- 

 mations cannot generally be supposed to take place in 

 a reversible manner, even although unlimited time be 

 allowed. Some progress has, however, recently been 

 made, and the experiments of Debray on the influence of 

 pressure on the evolution of carbonic anhydride from 

 chalk throw considerable light on the matter. By properly 

 accommodating the pressure and temperature, the con- 

 stituents of chalk may be separated or recompounded 

 without dissipation, or rather dissipation may theoreti- 

 cally be reduced without limit by making the operation 

 slowly enough. 



The possibility of chemical action must often depend 

 pn the density of the reacting substances. A mixture of 

 oxygen and hydrogen in the proper proportions may be 

 e.xploded by an electric spark at the atmospheric pres- 

 sure, and energy will be dissipated. In this operation the 

 spark itself need not be considered, as a given spark is 

 capable of exploding any quantity of gas. Suppose, now, 

 that previously to explosion the gas is expanded at 

 constant temperature, and then after explosion brought 

 back to the former volume. Since in the combination 

 there is a condensation to two-thirds, the pressure 

 required to compress the aqueous vapour is less than 

 that exercised at the same volume by the uncombined 

 gases, and accordingly work is gained on the whole. 

 Hence tlie explosion in the expanded state involves less 

 dissipation than in the condensed state, and the amount 

 of the difference may be increased without limit by 

 carrying the expansion far enough. It follow that beyond 

 a certain point of rarity the explosion cannot be made, as 

 it could not then involve any dissipation. But although 

 the tendency to combine diminishes as the gas becomes 

 rarer, the heat developed during the com.bination remains 

 approximately constant. 



It must be remembered that the heat of combination is 

 generally developed at a high temperature, and that 

 therefore work may be done during the cooling of the 

 products of combustion. If, therefore, it is a necessity of 

 the case that the act of combustion should take place at 

 a high temperature, the possibility of explosion will cease 

 at an earlier point of rarefaction than would otherwise 

 have been the case. 



It may probably be found that many mixtures which 

 show no tendency to explode under ordinary' conditions 

 will become explosive when sufficiently condensed. 



NOTES 



The Boimcr Zeiiuno publishes 'a letter of Dr. Seeliger, con- 

 taining the first detailed reports from the German party of 

 observers sent to the Auckland Islands to observe the Transit of 

 \'eiius. Dr. .Seeliger speaks of the weather in these islands as 

 the most wretched imaginable ; enough, he says, to drive an 

 astronomer to despair. " Clear evenings are very rare, and sun- 

 shine a phenomenon." On Dec. 9, at 12.45 r.M., " Venus was 

 to appear on the sun's disc ; one minute passes after another, and 

 still all is covered. At last the clouds thin a little, and without 

 dark glass we can easily see Venus, that had just entered on the 

 sun's disc. The two first contacts, which, however, were of less 

 value to us, were lost therefore. A quarter of an hour afterwards 

 a little gap shows itself in the clouds, the sun breaks through, 

 and we at once set to work, so as not to lose a single moment. 

 And now comes the wonder ! For nearly four hours the sun 

 remains completely free from clouds. In the east and in the west 

 thick clouds ; only where the sun stands it is clear. Hardly has 

 Venus passed off the sun's disc, therefore hardly have we com- 

 pletely succeeded with our measurements, when the sky is again 

 overcast all over. To-day the day is dull, as usual. As affairs 

 stand we shall very likely have to stop here two or two-and-a-half 

 months longer, because we have not yit been able to do an v. 

 thing for the other astronomical data, which are indispensable. 

 On the one hand it is hardly possible to do anything in this 

 climate at this time, and then we finished our general prepara- 

 tions only a long time after we thought we should do so." 



We regret to record the death of Carl Ludwig Christian 

 Becker, who has for so long been known to students of physical ^ 

 science in this country in connection with the firm of Elliott 

 Brothers. He was born at Ratzeburg, in the Grand Duchy 

 of Mecklenburg Strelitz, July 16, 1821, and received his general 

 education at the Gymnasium of his birthplace, of which his 

 fither was Rector. He studied his profession with Repsold at 

 Hamburg, Kraft at Vienna, and Steinheil at Munich, and came 

 to London in 1S49, joining the firm of Elliott Brothers in 

 1S58. Within the last few years he became a member of the 

 Society of Telegraph Engineers and Fellow of the Royal Astro- 

 nomical and Physical Societies. We believe that there is no 

 one who has pursued physical inquiries in England who will not 

 look upon his loss as that of a personal friend, while his skill in 

 providing new appliances for investigation reminc's us how often 

 the most important scientific work is dependent upon the skilled 

 mechanician. 



The Royal Academy of Medicine at Brussels has given its 

 opinion on the so-called "miracle," Louise Lateau, who, it is 

 said, by divine assistance abstains from taking food, and has 

 done so for years together. Moreover, this miraculous creature 

 has some wounds in her hands, side, and feet, which are said to 

 be true representations of those of Christ, and which bleed pro- 

 fusely every Friday. Dr. Virchow, the celebrated German 

 anatomist, has made her the subject of a little pamphlet, 

 " Ueber Wunder." The opinion of the Brussels Academy, which 



is quite in accordance with that of Dr. Virchow, is as follows : 



"Louise Lateau works and requires heat ; every Friday she 

 loses a certain quantity of blood by her wounds. When she 

 breathes, she exhales water vapour and carbonic acid ; her 

 weight has not decreased since she has been observed ; she 

 therefore consumes carbon which is not furnished by her system.- 

 Where does she take this carbon from ? Physiology simply 

 replies, 'She eats.' The alleged abstinence from all food of 

 Louise Lateau is contradictory to all physiological laws ; it is 

 therefore hardly necessary to prove that this abstinence is an 

 invention. Whoever alleges that Louise Lateau is not subject to 

 physiological laws, must prove it ; until this is done physiology \vill 

 denote the miracle to be a deception. Could Louise Lateau be 



