February 20, 1908] 



NA TUBE 



565 



those, the vast proportion, who will have no subse- 

 tjuent regular instruction in the subject, the method 

 -.uid mode of treatment of the author may be heartily 

 commended. It is, we learn, the outcome of actual 

 class work, modified by experience and the mutual 

 play of the minds of teacher and taught. The author 

 lias a belief in the especial value of " outdoor chem- 

 istry " as appealing to the interests of the learner, 

 ^nd there is an excellent chapter towards the end on 

 plant respiration and nutrition. 



One notices a few important omissions and errors. 

 The use of the spectroscope in chemistry is nowhere 

 idluded to. The mention of argon and its companions 

 In the air should be amplified or omitted. As it is, it 

 contains one of the few mistakes, in the statement 

 that the density of argon is forty times that of 

 hydrogen. Helium is not even referred to by name, 

 surclv a remarkable omission for an author addicted 

 lo "outdoor chemistry." We read, "The exact 

 specific gravity of oxygen ... is 1588 (H = i)- This 

 makes the atomic weight of oxygen I5'88. ..." But 

 these few blemishes in no way detract from the 

 ijeneral accuracy of the treatment. 



It is a pleasure to notice a book of this description, 

 for it indicates the serious and important place 

 chemistry is taking in the school curriculum. It 

 deserves a high place, not only in the school, but 

 generally as an excellent introductory first course, 

 tmderstanding by this term not a mere smattering of 

 the kind deemed sulhcient only a few years ago, but 

 :i course in keeping with the true position of the 

 science as a serious and profitable part of a good 

 modern education. 



Mlitiide Tables. Computed for Intervals of Four 

 Minutes between the Parallels of Latitude 31° and 

 f)o° and Parallels of Declination of 0° and 24°, de- 

 signed for the Determination of the Position Line at 

 all Hour .\ngles without Logarithmic Computation. 

 By F. Ball. Pp. xxxii + 241. (London: J. D. 

 Potter, 1907.) Price 15X. net. 

 The main purpose of these tables is to facilitate the 

 determination of the position line from an observation 

 of any heavenly body and to eliminate, practically, the 

 chance of errors of computation in the result. When 

 the idea occurred to the Rev. F. Ball he consulted the 

 Astronomer Royal, who consented to the employment 

 of several of the Greenwich computers on the work, 

 under the direction of Mr. Crommelin ; the accuracy of 

 the tables is therefore beyond suspicion. The tables 

 are computed for intervals of every four minutes 

 between latitudes 31° and 60° and parallels of declin- 

 ation 0° and 24°, and they enable the observer to 

 determine the position line at all hour angles without 

 having to solve any spherical triangle. This does 

 away with the necessity for logarithmic computations, 

 and so the probability of errors is eliminated. For 

 altitudes less than 70° it is expected that the tables 

 will give results accurate within 12" ; for greater alti- 

 tudes their use is not recommended. The author 

 hopes soon to publish a companion volume for latitudes 

 0° to 30°. 



Problems in Strciii^ni of Materials. By Dr. William 

 Kent .Shephard. Pp. vii + 70. (London: Ginn and 

 Co.. n.d.) Price h.v. 



Whillaker's Arilhmclic of Electrical Engineering for 

 Technical Students and Engineers. Pp. vii4-i59. 

 (London : \\'hittaker and Co., n.d.) Price \s. net. 

 To set students of applied science to work numerical 

 l)roblems involving thought in their subject is a good 

 test as to whether they understand the principles in- 

 voked. It is customary in many classes to associate 

 »he i.iboratory and lecture work with practice in 

 NO. 1999, VOL. 'J-j'\ 



solving such problems, and teachers will find in these 

 volumes many examples suitable for the purpose. The 

 first volume, in addition to 568 exercises, contains 

 some useful tables, but little in the way of worked-out 

 examples to guide the student is given and no answers 

 are provided. The second book, on the other hand, 

 contains seventy-two typical problems fully solved, and 

 a set of answers. 



.Ill Essay upon Disease: its Cause and Prevention. 



By Dr.' G. E. Richmond. Pp. i/i. (London: H. K. 



Lewis. 1007.) Price 2X. net. 

 The main object of Dr. Richmond's little book is to 

 point out the large number of diseases either spread 

 by food or directly due to impurities in food or articles 

 in common use. It is surprising to find a confession 

 in the preface to the effect that " the essay has been 

 written rather hurriedly," and unfortunate that no 

 index is provided. 



LETTERS TO THE EDITOR. 



\The Editor does not hold himself responsible for opinions 

 iwpressed 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 0/ Nature. 

 No notice is taken of anonymous communications.] 



Radium and the Earth's Heat. 



It has been shown by ihu Hon. R. J. Strutt and other 

 investigators that the materials composing the surface of 

 the earth contain on the average about 10-'- gram of 

 radium per gram, while about one-twentieth of this 

 amount is sufficient to account for the heat lost by the 

 interior of the earth by conduction. Mr. Strutt has there- 

 fore suggested that the interior of the earth contains less 

 radium per gram than the surface. It is interesting to 

 calculate what would happen if the whole earth contained 

 10-'" gram of radium per gram. If the specific heat of 

 the interior of the earth is taken to be o-i, and 1 gram 

 of radium is supposed to generate lOo calories per hour, 

 then it is easy to show that the temperature of the interior 

 of the earth would rise bv 10-^ degree C. per year if all 

 the heat generated by the radium were used up in raising 

 the temperature. 



If the temperature of the interior rose 100° C, it is 

 probable that the rise near the surface would be too small 

 to be detected, so that observations extending over at least 

 ten million years would probably be necessary to detect 

 the effect of the heat generated by radium even if the 

 whole earth contained 10-'- gram of radium per gram 

 and all the heat generated went to raise the temperature. 



I understand that geologists are inclined to think that 

 the temperature near the surface of the earth has not 

 altered much for many million years, but this is not in- 

 consistent with a rise of 10-^ degree C. per year in the 

 interior. It is, of course, quite possible that the specific 

 heat of the earth is considerably greater than o-i. The 

 high pressure in the interior probably makes the specific 

 heat larger than at the surface. 



Harold .\. Wilson. 



I MENTIONED the possibility which Prof. Wilson dis- 

 cusses in my original communication on radium in the 

 earth's crust in the Royal Society's Proceedings: but he 

 certainly shows that it is more worthy of attention than 

 I then thought it. 



On this theory it becomes necessary to suppose that the 

 primary stock of radio-active material in the earth — 

 uranium — has not been in existence for a longer time than 

 is required for the attainment of thermal equilibrium by 

 conduction, for we know that the uranium is wasting 

 away, and unless the supply is replenished it is clear that 

 the gradient of temperature must diminish, instead of 

 increasing as Prof. Wilson supposes. We cannot at pre- 

 sent form any notion as to how the uranium could come 

 into existence, so that any further development of the idta 



