NA TURE 



[June 2, 1904 



from English sources, and to have devoted more 

 attention to popular expositions than to the original 

 literature of the subject. The volume is conse- 

 quently not free from the faults that are almost in- 

 separable from a compilation of this kind, and the 

 arrangement of the matter is in places somewhat con- 

 fusing. But the author has made a sober and honest 

 atterript to give a simple explanation of a very com- 

 plex subject, and has attained a fair measure of suc- 

 cess. The figures are clearly and simply drawn, and 

 the full-page plates, which include reproductions of 

 the spectra of radium, calcium and helium, and of 

 Sir William, Huggins's two series of spectra, are 

 valuable features of the book. 

 Second Stage Botany. Bv J- M. Lowson. Pp. viii + 



452. (London : W. B. Clive, 1904.) Price 3s. 6d. 

 The syllabus of the second stage examination in botany 

 of the Board of Education has been judiciously framed 

 on broad lines, and those students generally shape best 

 who possess a reasonable knowledge of the structure 

 and activities of plants and apply that knowledge in 

 their answers. In the preparation of students for this 

 examination the primary object should be to emphasise 

 leading principles, and further to stimulate reflection 

 by making the student observe many facts for himself. 

 Instead of this one finds in the book under notice the 

 usual attempt to supply directly all the information 

 required to answer the manifold questions which are 

 possible, and important facts are lost in the mass of 

 detail. In the latter part of chapter ii., which deals 

 with tissues, the most essentia! fact is the importarice 

 of the vascular tissues as continuous conductive 

 strands, but this is relegated to one of the final sections, 

 which is reached after wading through descriptions of 

 meristems, stereid bundles, sclerotic cells, &c. The 

 chapter on the leaf bristles with terms, including the 

 " incubus " of phyllotaxis, but any suggestions as to 

 the reasons for the variety of form are considered un- 

 necessary. Another defect in the book is the inclusion 

 of antiquated terms and ideas, of which the most 

 noticeable, because it is accompanied by a diagram 

 {Fig. 105), is the existence of centrospheres in Phanero- 

 gams. The description of " double-fertilisation " is 

 peculiar; on p. 199 it is stated that the generative cells 

 pass down into the pollen tube, and one cell fuses with 

 the oosphere; "the fate of the other generative cell 

 is described on p. 304." One is tempted to find a 

 correlation between this method of incorporating the 

 result of recent research and the statement which 

 appears in the introduction, that a large portion of 

 this work has already appeared in the author's " Text- 

 book of Botany." 

 Les Frontiircs de la Maladie. Maladies latentes et 



Maladies atteruies. By Dr. J. H^ricourt. Pp. 



xi + 285. (Paris: Ernest Flammarion, 1904.) Price 



3.50 francs. ■ 

 Although in well marked cases health and sickness 

 are distinct and opposite conditions, in a large number 

 of instances the boundary between the two is indefinite, 

 the one passing insensibly into the other, and it is with 

 this borderland that the author of the work under 

 review deals. Commencing with dyspepsia, he shows 

 how this may pass on into more grave conditions, and 

 by natural stages finally comes to consider the mild 

 types of such infective diseases as scarlatina, enteric 

 fever, and diphtheria, which in their mildest forms 

 cause little disturbance, and may pass unnoticed and 

 undiagnosed. 



Among others, an interesting chapter is devoted to 

 a consideration of how epidemics of disease spon- 

 taneously die out. As treating of a little studied 

 branch of medicine, the book is suggestive and to be 

 recommended. R. T. Hewlett. 



NO. 1805 , VOL. 70] 



LETTERS TO THE EDITOR. 



''The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.] 



e<p Lines of Total Heat. 



I THINK that 6<f) diagram curves showing constant total 

 heat, although often drawn by students, have never yet been 

 published, and I venture to ask you to publish a set made 

 more carefully than usual by one of my students, Mr. 

 A. W. Steed. Total heat is intrinsic energy -j- pv, so that 

 for steam it is what Regnault called his total heat. In 

 the figure I have indicated the pressure, but of course the 

 ordinate is proportional to temperature and the abscissa is 

 entropy. Along OW the stuff is all water. Along SS the 

 stuff is all saturated steam. The thin lines, like AB, show 

 the stuff maintaining the same fractional dryness ; for 

 example, along AB the stuff is 03 of steam, 07 of water. 

 Along the thicker lines, like AE, the stuff has constant total 

 heat. 



Many people have the notion that when steam is throttled 

 it is very greatly dried. Of course the drying is greater if 



the place of throttling is well protected from loss of heat 

 bj' a non-conducting covering, and in this case total heat 

 remains constant. Now if the line DC is looked at, it 

 will be seen that steam which is 90 per cent, dry at 300 lb. 

 pressure, if throttled to 150 lb. pressure is about 93 per 

 cent, dry, and if throttled to 50 lb. pressure is about 

 954 per cent. dry. Thus the drying effect is not very 

 great. 



The effect is evidently more marked with very wet steam. 

 Thus, looking at AE, steam 30 per cent, dry at 300 lb. 

 pressure becomes 42 per cent, dry if throttlfed to 50 lb. 



The lines show at once how much steam at any pressure 

 will result on the Halpin system of storage from each pound 

 of stored hot water. Thus imagine a total heat line from 

 the point W in the figure. A pound of water stored at 

 300 lb. pressure and reduced to 150 lb. pressure will 

 generate about 0-07 lb. of steam. 



I need not mention the other important applications of 

 this diagram. To the right of SS, in the superheated part, 

 lines of constant total heat are horizontal, being lines of 

 constant temperature. John Perry. 



Royal College of Science, South Kensington, S.W. 



