78 



NATURE 



[Afay 26, 1 88 1 



By the use of Gimmingham's form of pump the exhaustion can 

 be increased in a very short time, and the readings all obtained 

 from one cylinder an inch in diameter. Three series of readings 

 were tal^en agreeing very well with each other. At fir.'-t there 

 were discrepancies, owing to the porosity of the cylinder not 

 bein" noticed, but these disappeared when care was taken. The 

 temperatures were not corrected, as the results were not intended 

 for publication, as I expected some other worker to repeat the 

 experiment, but that not being the case I give the numbers as 

 they are, premising that the temperatures, if corrected, would be 

 6° or 7° higher for the upper and 4° to 6' for the lower ones. 

 The following are the numbers obtained : — 



Pressure in Temperature of 

 millimetres. volatilisation. 



40 233 



30 228 



20 223 



10 214 



5 205 



o 1S5 



Temperature of 



volatilisation. 



245 

 222 

 5 210 



But I do not place the same confidence on these numbers, as 

 they were obtained in ignorance of the porosity of the solid ; but 

 they confirm the others. It appears from the above that mercuric 

 chloride is no exception to the geneial law which makes the 

 volatilising point rise or fall with tlie pressure. The low latent 

 and specific heats of mercuric chloride nnke it not nearly so 

 suitable an exponent of the truth of Regnault's coiclusions as 

 water ; the latter allowing of a whole hour's continued experi- 

 ment. I think after these experiments the idea of being able to 

 raise solids in vacuo to tempera! in-es above their ordinary volati- 

 lising or boiling points may lie dismissed as inadmissible, except 

 it may be in some rare case of allotropy. J. B. Hannay 



Private Laboratory, Sword Street, Glasgow 



The Conservation of Electricity 



By the kind permission of Messrs. Macmillan and Co. I am 

 allowed to quote the following paragraph from the preface to 

 my " Elementary Lessons in Electricity and Magnetism," shortly 

 to be published by them in their School Class Books Series, and 

 now in the press. The preface is dated " March, 1881." 



" The theoiy of Ele-tricity adopted throughout is that Electri- 

 city, whatever its nature, is on,; not /7ao : that Electricity, what- 

 ever it may prove to be, is not maffer, and is not energy : that it 

 resembles both matter and energy in one respect, however, in 

 that _it can neither be created nor destroyed. The doctrine 

 of the Conservation of Matter, established a century ago by 

 Lavoisier, teaches us that we can neither destroy nor create 

 matter, though we can alter its distribution and its forms and 

 combinations in innumerable ways. The doctrine of the Con- 

 sen'ation of Energy, which has been built up by Helmhoitz, 

 Thomson, Joule, and Mayer, during the last half century, teaches 

 us that we can neither create nor destroy energy, though we may 

 change it from one form to another, causing it to appear as the 

 energy of moving bodies, as the energy of heat, or as the static 

 energy of a body which has been lifted against gravity or some 

 other attracting force into a position whence it can run down, 

 and where it has the potentiality of doing work. So also the 

 doctrine of the Conservation of Electricity, which is now growing 

 into shape,' but here first enunciated under this name, teaches 

 us that we can neither create nor destroy electricity, though we 

 may alter its distribution — may make more to appear at one 

 place and less at another — may change it from the condition of 

 rest to that of motion, or may cause it to spin round in whirlpools 

 or vortices which themselves can attract or repel other vortices. 

 According to this view all our electrical machines and batteries 



are merely instruments for altering the distribution of electricity 

 ^ Tliis is undoubtedly the outcome of the ideas of Maxwell and of Fara- 

 day as to the nature of electricity. Jt has nowhere been more excellently or 

 pithily put into shape than in a discourse delivered by Dr. Oliver J. Lodge 

 before the London Institution, " On the Relation between Light and 

 Electricity," December 16, 18S0 (Natukp, vol. xxiii. p 302). 



by moving some of it from one place to another, or for causing 

 electricity, when heaped up in one place, to do work in returning 

 to its former level distribution. Throughout these Les.ons the 

 attempt has been made to state the facts of the science in lan- 

 guage consonant with this view, but rather to lead the young 

 student to this as the result of his study than to insist upon it 

 dogmatically at the outset." 



The above paragraph is published at the present time because, 

 since the date wh^-n my manuscript was sent to the publishers, a 

 memoir has been presented to the Academie des Sciences bearing 

 the title, " Sur le Principe de la Conservation de I'Electricite, ou 

 seconde Principe de la Theorie des Phenomenes Electriques." 

 Of this memoir, which is by M. G. Lippmann, only a brief 

 extract has as yet been published in the Compies rendus of the 

 sitting of May 2, when it was read. In that short extract the 

 general doctrine of the conservation of electricity is laid down 

 \\ ith considerable clearness, and an elegant analytical expression 

 of it is given in the briefest form, the author promising some 

 examples of its application to the prediction of new and impor- 

 tant phenomena. The publication of the complete memoir of 

 M. Lippmann will no doubt be a>\ aited with interest. 



As my manuscript was placed in the hands of Messrs. Mac- 

 millan and Co. on the very day when the above extract was 

 written, the phraseology used by M. Lippmann must have been 

 adopted by him in entire independence of me. Since some 

 weeks must elapse before my " Elementary Lessons " will be in 

 the hands of the public, I wish to avoid, meantime, all chance 

 of misunderstanding by taking the earliest opportunity, firstly, 

 of making this acknowledgment, which is due to M. Lippmann, 

 and secondly, of establishing my right to use the language of 

 my preface as to the explicit enunciation of the doctrine of the 

 Conservation of Electricity. SiLVANUS P. Thompson 



University College, Bristol, May 19 



The Florence Herbarium 



I BEG to forward to you the inclosed protest of the 

 botanists of Florence against the proposed removal of the 

 Herbarium and adjoining Botanical Garden at Florence to a 

 new locality in that city. 



It is well known to all botanists who have visited that city 

 that, taking into account the importance of the herbarium, the 

 admirable building in which this and the other collections are 

 lodged, and the annexed botan'cal garden, the establishment at 

 Florence deserves to rank amongst the first in the world, and is 

 indeed scarcely second to any except that at Kew. It has an 

 especial interest in the eyes of Englishmen, owing to the fact 

 that it includes the invaluable collections of the late Mr. Barker 

 Webb, which include, besides the type specimens of the Canary 

 Island flora and of his other works, those still more important 

 of Labillardiere, of Rinz and Pavon, and of Desfontaines, whose 

 herbaria all passed into his hands. 



Although well acquainted with the Florence Museum, and 

 disposed to believe that it would be difficult to find another 

 locality equally well adapted for the purpose, I was unwilling to 

 express any opinion on the subject without full information as 

 to the new arrangements proposed in substitution for those now 

 so excellent. 



Within the last month my friends Sir Joseph Hooker and 

 Dr. Asa Gray have visited Florence, and have carefully examined 

 the present building and its appurtenances, and also the sites to 

 which it is proposed to remove the herbarium and botanic 

 garden. I learn that they have expressed an unqualified opinion 

 that the proposed new tiuilding is altogether unsuited for the 

 purpose, and would too probably tend to the injury and ultimate 

 loss of the herbarium, whde the site of the proposed botanic 

 garden is also an unfavourable one. 



Sir Joseph Hooker has written a full statement of his views 

 to Prof. Came], recently appointed Director of the Botanical 

 Museum, w-ho has not, I believe, as yet published his opinion on 

 the subject. 



Under these circumstances I venture to hope that you will 

 publish the accompanying document, with a view to prevent the 

 accomplishment of a design so injurious to natural science. 

 Those who wishjto associate their names with the protest are in- 

 vited to send them to M. E. Sommier, Lung'Arno, Corsini, 

 Florence. John Ball 



10, Southwell Gardens, London, S.W., May 20 



