NATURE 



[March 2, 1916 



his " Manual " the official scheme included the pro- 

 vision of a volume of plates to illustrate some 

 portion of the species described. Two sugg^estions 

 occurred to those who had urged the undertaking. 

 One was to reproduce on a reduced scale the un- 

 published engravings prepared to accompany the 

 descriptions by Solander of plants collected during 

 Captain Cook's first visit to New Zealand; the 

 other was to employ afresh the beautiful illustra- 

 tions which accompany Hooker's "Flora Novae- 

 Zelandiae." Both suggestions possess the merit 

 attaching to pious inspirations, though in reality 

 both owed their origin to the hope they held out 

 of enabling the Dominion Government to solve a 

 serious practical difficulty. This difficulty is due 

 to the circumstance that as yet there is not in 

 New Zealand a demand for work of the kind suffi- 

 cient to induce resident artists to devote them- 

 selves to the very special occupation of preparing 

 and reproducing figures of botanical subjects. 

 Fortunately, we think, the demand for the 

 " Flora " itself was so urgent that it was decided 

 to leave the question of illustrations in abeyance 

 until the text should be completed. That question, 

 however, was in the interval carefully considered 

 in all its bearings. For reasons which seem un- 

 answerable, both suggestions were set aside. It 

 was resolved that the " Illustrations " should be 

 new ones, educational in character, expressly 

 drawn for the work, and so designed and executed 

 as to be of use in the study and identification of 

 the plants portrayed. The practical difficulty was 

 frankly recognised, and was overcome by the 

 employment of an artist, a lithographer, and a 

 printer in England, while arrangements were 

 made for the supervision of their work, at every 

 stage, by an English botanist. 



The two handsome volumes of " Illustrations of 

 the New Zealand Flora " now before us show how 

 satisfactory these arrangements have been ; the 

 artist, whose name appears on the title-page, the 

 lithographer, Mr. J. N. Fitch, and the printers, 

 Messrs. West, Newman, deserve equal commenda- 

 tion for the excellence of their work. In his 

 choice of a supervising colleague, whose name 

 also appears on the title-page, the author of the 

 text has been especially fortunate; Mr. Hemsley 

 has fulfilled his part with remarkable judgment, 

 and, as the author explains, has often been able 

 to make comparisons of the material actually 

 figured so as to confirm its identity with the type 

 of the species concerned. The subjects of the 250 

 plates have been so selected by Mr. Cheeseman 

 that they illustrate satisfactorily the main features 

 of the New Zealand flora. No really important 

 genus or group of plants is left unrepresented, nor 

 is any latitude or altitude of the Dominion inade- 

 NO. 2418, VOL. 97] 



quately dealt with. The descriptive matter which 

 accompanies each plate is clear and concise, singu- 

 larly free from technical terms, and replete with 

 information of lx>tanical, economic, and historical 

 interest. The work is worthy of the reputation 

 of all those concerned in its production, and while 

 it affords proof, were this needed, that New Zea- 

 land can command competent botanical assistance, 

 it also shows that the Dominion enjoys an en- 

 lightened administration which is fully aware of 

 this fact. 



NEW AMERICAN STEAM TABLES. 

 Properties of Steam and Ammonia. By Prof. 

 G. A. Goodenough. Pp. vii+ 108. (New York : 

 J. Wiley and Sons, Inc. ; London : Chapman 

 and Hall, Ltd., 1915.) Price 55. 6d. net. 



THESE tables are a great improvement on 

 previous American work in the matter of 

 thermodynamic method and consistency, but the 

 expressions employed for calculating the tables 

 are too complicated to be of practical use for 

 other purposes, though comparing favourably with 

 many empirical formulae. The author assumes a 

 characteristic equation of the type, 



V-b = RT/p - (i + sapy^)m/T^, 

 and deduces consistent expressions for the total 

 heat and the entropy, according to Callendar's 

 method, by the aid of a formula for the specific 

 heat at zero pressure. He objects to Callendar's 

 equation on the ground that it makes the iso- 

 thermals straight lines on the pv,p diagram, 

 which is well known to ]yc a good approximation 

 at moderate pressures over the experimental range 

 from 0° to 200° C, but begins to fail at higher 

 pressures. Linde introduced the factor (i +ap) in 

 the last term to give the desired curvature to the 

 isothermals at high pressures. His equation has 

 been widely adopted in America, but is most un- 

 satisfactory, because it would make steam become 

 a "pluperfect" gas (pv increasing with p at con- 

 stant t) at a temperature of 400° C, a few degrees 

 above the critical point, which is impossible. The 

 form assumed by Prof. Goodenough escapes this 

 objection, and gives "reasonably good agree- 

 ment " with throttling experiments, but appears 

 to lead to excessive curvature of the isothermals 

 at low pressures, where they should be very nearly 

 straight, and also gives deficient curvature at high 

 pressures near the critical point, besides making 

 no allowance for the well-known fact that the 

 curvature must change sign at a temperature not 

 far above the critical. 



There are many ways in which Callendar's 

 equation may be modified to meet these conditions 

 and give good agreement with the saturation 



