ytme lo, 1875] 



NATURE 



107 



the work under notice, "We always receive with pleasure sug- 

 gestions for the improvement of this publication, and within 

 reasonable limits never allow either trouble or cost to prevent 

 the adoption of all which in any way commend themselves to 

 our judgment." 



Your suggestion is as follows : — 



" The publication of the monthly as well as the annual 

 amounts of rain for the whole of the 1,700 stations is very 

 desirable, and it is hoped that in an early issue of the * British 

 Rainfall ' it will be done." 



I shall be glad if you will allow me to supplement the data 

 which were before you when the above paragraph was written 

 by some other facts, and to learn from your pages whether or 

 not this fuller information induces any modification of your 

 views. 



As I (whether fortunately or unfortunately I need not say) 

 have to pay my own printer's bills, I always keep them as low 

 as possible ; hence, the publication being an annual one, state- 

 ments made in one volume are rarely repeated in the next. 

 Therefore, probably, your reviewer was not aware of the prin- 

 ciples upon which the tables of monthly rainfall (pp. 140-145) 

 are compiled, viz., to give one station in every county in the 

 British Isles, and two in a few of the larger ones, such as York, 

 Inverness, and Ross. I may add en passant that these tables 

 give the monthly fall at 108 stations, while the Registrar- 

 General of England is satisfied with forty-four, and of Scotland 

 with fifty-five ; so that my table exceeds both together. That, 

 however, is of little moment. [For your own information, I 

 enclose a map with these 108 stations plotted.] 



In the next place, I must refer to "British Rainfall, 1871," 

 IP- I35~I38» where the question of publishing additional monthly 

 returns is discussed at length, and the method of computing the 

 monthly fall from the percentage tables (which are given every 

 year) is explained and illustrated by a completely worked-out 

 example. 



To this let me add that returns from 150 other stations are 

 published monthly in my Meteorological Magazine, and that up 

 to the present time another very large series (143) has been 

 printed biennially in the Reports of the British Association. 



If it is the opinion of yourself and of others competent to judge 

 that still more is necessary, more shall be done ; but it must be 

 borne in mind that the accurate (and without accuracy figures are 

 worse than useless) printing of 20,400 values involves a great 

 expenditure both of time and of money. I do not quite know 

 whence either the one or the other is to be obtained. 



G. J. Symons 



[It was just because of the inadequacy of one station in each 

 county of the British Isles, and two in the larger counties, to 

 represent the rainfall, even though these be supplemented by 

 Mr. Glaisher's forty-four stations, the Scottish Meteorological 

 Society's two hundred odd, and by Mr. Symons himself in his 

 Magazine and in the British Association Reports, that we stated 

 it to be very desirable that the monthly as well as the annual 

 amounts of rain for the whole of the 1,700 stations were pub- 

 lished. The method of computing the monthly (all from the 

 percentage tables referred to in "British Rainfall, 1871," pp. 

 135-138, does not supply what is desiderated. It is tile capri- 

 ciousness of the distribution of the rainfall and its important 

 bearings on many practical questions which render so desirable 

 a knowledge of the actual monthly amounts in particular locali. 

 ties. Since what is desired would be an invaluable contribution 

 to British Meteorology, we earnestly hope that Mr. Symons 

 will be induced to supply it, and that in that case he will receive 

 substantial support in carrying on a work so important.] 



Equilibrium of Temperature in a Vertical Column 

 of Gas 



I OBSERVE that Mr. R. C. Nichols, in his letter to Nature 

 (vol. xii. p. 67), admits that the mean energy of molecules " way " 

 remain the same at all points of a vertical column. It is not 

 difficult to show that it vmst do so if the velocities are distributed 

 among the molecules according to the exponential law. 



As I have never seen any direct proof of this in English I 

 extract the following from Boltzmann. 



In order not to take up too much of your space, we will take 

 the simplest case, and suppose the molecules to be equal elastic 

 spheres, moving in a vertical tube with elastic base and sides. 

 Let them be acted upon by vertical forces, the potential of which 



at height x above the base is / {x). Assume first that no en- 

 counters take place between the molecules, and let the number 

 of molecules at the base, the energy of whose vertical velocity 



is v^, be Ce '■-■ where C and k are constants. For each molecule 

 the sum of the potential and kinetic energies is constant. 



And as the horizontal velocities are constant, it follows that 

 for each molecule the sum of the potential energy and the energy 

 of vertical velocity is constant. That is, the energy of 

 vertical velocity is diminished by/(;r) in the ascent from the 

 base to x. 



Therefore the molecules which at height x have u^ for energy 

 of vertical velocity are the same identical molecules which at 

 the base have u^ + f{x) for energy of vertical velocity. 



Their number is therefore Ce" *^ that is e a^' Ce"*^ * 

 Therefore the nimiber of each class at x is tl:e same as the 

 number of the same class at the base multipliel by the factor 



Evidently the mean energy is the same at all points of the 



tube, and the density only varies, and is represented by e ''" * 



Again, still precluding encounters, let the velocities of the 

 molecules in each of two horizontal directions at right angles to 

 each other be distributed according to the same law as the 

 vertical. And further, let the chance of a molecule having given 

 horizontal velocity in either direction be independent of its 

 velocity inthe other horizontal direction or in the vertical. The 

 same distribution and independence will be maintained through- 

 out the tube. And we see that force has no tendency to 

 disturb it. 



Maxwell has shown that among such molecules as we have 

 supposed encounters have no tendency to disturb the given dis- 

 tribution, which must therefore remain undisturbed though force 

 and encounters both be present. S. H. BURiiURY 



Primine and Secundine 



Will you allow me to avail myself of your pages as a means 

 of pointing out to those who have purchased the English edition 

 of " Sachs's Text-book of Botany" an unfortunate error which 

 Prof. Oliver has been so good as to point out to me ? 



On p. 501 the inner coat of the ovule is identified with the 

 "Primine" of Mirbel, and the outer with the " Secundine." 

 The application of these terms is exactly inverted. The con- 

 fusion easily arises from the fact that the secundine is developed 

 first and the primine second. Mirbel, however, ignorant of, or 

 disregarding that fact, numbered his structures from without 

 inwards. The outer coat he termed the primine, the inner the 

 secundine, the nucleus the tercine, and so on to quartine and 

 quintine. 



Except for the sake of accuracy the matter is of no essential 

 consequence. Those who study the coats of ovules may well be 

 indifferent to Mirbel's perplexing terms. But in these days, when 

 students are expected for examination purposes to know about 

 the names of things rather than about things themselves, it 

 might lead to deplorable consequences, of which I hasten to 

 relieve myself of the responsibiUty, 



W. T. Thiselton Dyer 



American Indian Weapons 



In Col. Lane Fox's Catalogue of his Anthropological Collection 

 he quotes Schoolcraft as saying, " There is no instance amongst 

 the North American Indians in which the war-club employed by 

 them is made of a straight piece, or has not a curved head. " I 

 send you a drawmg (Fig. i) of a club in common use among 

 the Numas, or Indians of the Great Interior Basin, embracing 

 Shoshones, Utes, Pueblos, &c., which will no doubt interest 

 Col. Fox and others, not only on account of its extreme sim- 

 plicity of form, but also of its method of use. It might 

 be called appropriately a " face-masker," being grasped with 

 the bulb next to the little finger, and thrust into the countenance 

 of the foe. Major Powell sent a number of these to the Smith- 

 sonian Institution. They are of one piece of wood, generally 

 mezquite, either very rude or quite smoothly polished, and are 

 w»rn attached to the wrist by a leather thong. They vary in 

 length from eight inches to fourteen. These same tribes use a 

 simpler " slimg shot " tJiai^he one described in Col. Fox's Cata- 



