Nov. 13, 1873J 



NA TURE 



27 



almost impossible to carry out any scientific or literary inquiry 

 in a complete manner, without resorting to the great national 

 museum. There are doubtless many things which the Trustees 

 have not done, but is it a slight matter lliat they have given us, 

 on the whole, by far the most extensive and complete body of 

 collections anywhere brought together in the world ? The 

 library and reading-room alone are enough to do honour to their 

 maiiagement, and it is almost impossible to fathom the degree 

 in which this library assists every kind of inquiry. When we 

 are least aware, we are often enjoying the fruits of investigation in 

 that library ; the late Prof Boole, for instance, spent the last few 

 months of his life in the Museum, pursuing an exhaustive inquiry 

 into previous writings on the subject of Differential Equations. 



As regards the other collections, I presume that no cne will 

 call in question their enormous extent ; and the fact tliat they are 

 not adequately lodged and displ.ayed as yet, is due to their very 

 vastness, and to the fact that Government would not, until lately, 

 afford the money for the new buildings. As regards the real 

 interests of original inquiry, too, (.oniparatively little harm is 

 done by the want of room for exhibition, since bond fide 

 scientific students can always obtain access to the collections. 



I am far from denying that the officials who have conducted 

 the South Kensington Museum have, by an enormous expendi- 

 ture of public money, collected together a great quantity of 

 beautiful objects of art, and have thus not only afforded oppor- 

 tunities for art study, but have made this museum a very agree- 

 able and fashionable lounge. But I must protest agamst the 

 notion, apparently countenanced in N.^TURE, that the scientific 

 value and worlc of a national museum is to be measured by the 

 number of millions of persons who saunter through the galleries. 

 No doubt the utility of a museum in affording popular instruc- 

 tion and elevated amusement to large masses of people is very 

 considerable, but this popular work is altogether of a different 

 order from the strictly scientific object of collecting together all 

 the products of intellect and of Nature. It is an unavoidable 

 misfortune of the best and highest work in science that it is 

 quite unobtrusive. The public is struck by the thousands who 

 crowd the decorated galleries of South Kensington. There is 

 nothing to attract public attention in the two or three hundred 

 bookworms patiently plodding through the books in the Museum 

 library, or the few students turning over the drawers of the zoo- 

 logical, botanical, mineralogical, numismatic, and other collec- 

 tions. But in Nature, which has so powerfully advocated the 

 necessity of promoting original research in this country, I should 

 expect, more than anywhere else, to find a due appreciation of 

 the noble work which is being carried out by the British Museum 

 trustees, and by the staff of eminent scientific and literary men 

 who are employed under their direction in promoting almost 

 every branch of literature and science. We have heard many 

 complaints of the apathy displayed by Government in the |)romo- 

 tion of science. The existence of the British Museum is the best 

 answer to that complaint. As regards those branches of science 

 which demand the use of large collections, it mry be regarded 

 as the great national laboratory ; and if scientific man do not 

 make adequate use of it, that is their fault and not that of the 

 trustees. W. Stanley Jevons 



[Our opinion of the immense importance to research of the col- 

 lections of the British Museum is quite in accordance with the 

 above letter of our esteemed correspondent, and if he will read 

 the article again he will see nothing in it to indicate any differ- 

 ence of opinion. Indeed we regard the positions of the scientific 

 men in the British Museum as positions of endowed research, 

 and positions, moreover, which have amplyjustified it, miserable 

 as the amount is in many cases. Our objection is to the existence 

 of trustees not represented by a Minister, and to the action of the 

 trustees, who have not expanded the area of the utility of the 

 collections, and who have cared so little for the men of science 

 working under them and the collections themselves that the 

 former are underpaid and the latter are much less useful than 

 they might be. Mr. Jevons concedes the whole point when he 

 refers to the money so properly spent at South Kensington ; for 

 had the British Museum been under the same Minister, money 

 would have been spent there too. The money must be Spent 

 unless we are to sink to the level of — well, let us say Morocco ; 

 and it is to prevent this that the proposed transfer has been sug- 

 gested. — Ed.] ■ 



On the Equilibrium of Temperature of a Gaseous 

 Column subject to Gravity 

 In Nature, vol. viiL P.4S6, Mr. Guthrie asks the question, 

 " Is thre no possibility of testing the nature of thermal equili- 

 brium of a column of still air?" I think to this question an 



answer may be given, which, though indirect and imperfect, 

 will perhaps decide the controversy on the above subject. 



If gravity causes in the temperature of a gaseous column the 

 difference, which Mr. Guthrie thinks it does, that difference must 

 be in proportion to the height of the column, and in inverse pro- 

 portion to the specific heat of the gas. Hence it follows that, if 

 two equal columns of different gases, both under the same ther- 

 mal influence, are joined at their lower parts by a thermo-electric 

 pile, the side of this pile, which is surrounded by the gas with 

 the highest specific heat, must be constantly cooler than the 

 other side. The result of my experiments respecting this, is the 

 confirmation of Mr. Guthrie s opinion. The description of these 

 experiments, and a theoretical treatise on the subject, have been 

 in the hands of Prof Poggendorff since the beginning of last 

 June, ai;d will be published in an early number of his Amialen. 



I hope that my experiments will induce others to try them in 

 the same or in another manner, in order to bring the question 

 concerning the influence of gravity on the thermal equilibrium 

 to a final decision. Should it prove in favour of Mr. Guthrie's 

 theory, as I believe it will, this theory, represented till now only 

 by a very small minority, although it was broached twenty 

 years ago by Waterston,* will give rise to resultst which may 

 perhaps clear up many of our ideas about Kosmos. 



The argument which Prof Clerk-Maxwell has brought against 

 Jlr. Guthrie in N.iture, vol. viii. p. 85, does not appear to 

 me to be generally correct. He says:— In a given horizontal 

 stratum of a gaseous column subject to gravity, a greater number 

 of molecules come from below than from above to strike those 

 in the stratum, because the density of the gas is greater below 

 than above. Certainly the number of molecules, which enter 

 into such a stratum during a certain time, depends upon the 

 density of the gas, but besides this, it depends upon the proba- 

 bility of entering into it, which exists for each molecule. Now, 

 this probabdity is not only dependent upon the distance of a 

 molecule from the stratum, upon its velocity, its direction and 

 its encounters with other molecules, but also upon the very fact 

 of its being above or below the stratum. 



Gravity continually tends to diminish thedis'ance between any 

 horizontal stratum and each molecule which is above the stratum, 

 and continually tends to increase the distance between the 

 stratum and each molecule which is below. Hence it follows 

 that the probability of entering into the stratum will be greater 

 for a molecule which is above than for one below, if, in the case 

 of both, all other circumstances are equal. For example, con- 

 sider two molecules, which in a given moment move with the 

 same velocity and in the same direction on the two sides of the 

 stratum ; if this direction is horizontal like the stratum, and if 

 in the given moment the distances of the molecules from the 

 stratum are both very small, in the next moment the molecule 

 above the stratum will have entered into it, while that one below 

 will have removed from it. 



In the case of the density being greater below the stratum than 

 above, more molecules would enter it from below, if gravity did 

 not exist. But under the influence of gravity, the effects of the 

 difference in density can be balanced by those of the above- 

 mentioned difference in the probability, which exists for each 

 molecule of entering into the stratum during a certain time. I 

 even consider this last difference to be the dynamical cause of 

 the difference in density. 



Westend, near Berlin, Oct. 20 G. Hansemann 



Periodicity of Rainfall 



As far as my own figures are concerned, the reply to Mr. 

 Meldnim's question is very easily afforded. I agree with him 

 that it is undesirable to use averages deduced from groups of 

 stations variable both in the number and locality of their com- 

 ponents. The observations which I quoted were those of a 

 single station, H.alton, St. Philip, Barbadoes. 



With respect to the general question, I regret being unable to 

 share Mr. Meldrum's evident enthusiasm, and that a very 

 different opinion has been published in the Ziilschrijt, by 

 Dr. Jelinek, one of the most eminent meteorologists of the 

 present day. It may be convenient to some readers to be in- 

 formed that an abstract of Dr. Jelinek's article is given in 

 " British Rainfall, 1872," together with a general r<.OT//// of th 3 

 state of the question up to the date of its publication. 



Camden Square, Nov. i G. J. Symons 



* In " On Dynamical Sequences of Kosmos." 



+ I fiave expounded some of tliese results in an abstract mechanical form 

 in "Die Atome und ilire Uencsiirigen" (Coin Lengfcld'sctie Buchhandlung, 

 ■ 871). 



