460 



NATURE 



[December 26, 191 2 



hints in picture form of "how to do it," being a 

 useful set of wrinkles for the beginner. 



Space does not allow us to do more than name 

 such useful items as the year's progress, working 

 formula, tables of various kinds, &x., as are 

 brought together in this storehouse of photo- 

 graphic information. Excellent indices make it 

 quite easy to find anything contained in the volume, 

 and the usual price of one shilling makes the issue 

 available to everyone. 



(2) The second book has for its object the pre- 

 sentation of a selection of articles on current 

 photographic topics combined with reproductions 

 of numerous specimens of photographic work. 



The editor evidently had a very large amount 

 of material to handle, and his selection contained 

 in this volume should meet the requirements of 

 most photographers. The list of contributors is 

 quite large, and the subjects dealt with exceedingly 

 varied, so that the volume forms a series of short 

 essays on many very useful hints in different 

 branches of the subject. The illustrations are good 

 throughout, and the frontispiece is a fine repro- 

 duction on buff linen. The last portion of the book 

 is devoted to a typical collection of formvilae and 

 tables selected from the working methods of prac- 

 tical photographers. 



OUR BOOKSHELF. 

 Studies in Light Production. By Dr. R. A. 

 Houston. Pp. iii+115. {The Electrician 

 Series.) (London : The Electrician Printing and 

 Publishing Co., Ltd., n.d.) Price 55. net. 

 The publication in one volume of Dr. Houstoun's 

 papers on artificial illumination will be welcomed 

 by all those interested in that subject. The collec- 

 tion consists of ten chapters which have appeared 

 in The Electrician, together with two others. It 

 may at once be said that the contents are not only ex- 

 tremely interesting, but will also serve as a useful 

 and important handbook for lighting engineers. 



The intention of the author has been to collect 

 information respecting the various illuminants at 

 present in use for purposes of comparison and 

 with the view of suggesting the lines upon which 

 future progress may be made. Thus we find 

 following the first two chapters (which are devoted 

 to the consideration of the energy spectrum and 

 the black body) a chapter on each of the following 

 light sources : flames, the Welsbach mantle, the 

 carbon glow-lamp, the arc, the Nernst lamp, 

 metallic filament lamps, and the mercury arc. 

 Comparisons of the luminous and radiant 

 efficiencies are given, showing how great improve- 

 ments in these have been made in recent years. 

 In chapter x. the author discusses the question of 

 the light of the future particularly with reference 

 to the possible use of vacimm tubes containing 

 nitrogen, or, according- to Claude, neon by prefer- 

 ence. Some very striking figures are given which 

 certainly seem to indicate the probability of great 

 NO. 2252, VOL. 90] 



saving of energy by this mode of lighting. Atten- 

 tion is also given to fluorescence, and, although 

 the author advises caution in this case, this also 

 may some day be used. 



Chapter xi. is a reproduction of Dr. Houstoun's 

 Royal Society paper on the absolute measurement 

 of light, the proposal being to measure light by 

 means of a thermopile which receives the energy 

 surviving the passage through a suitable filter, 

 i.e. one which cuts off the infrared and ultraxiolet 

 and is transparent to the various luminous radia- 

 tions in proportion to their visibilities. Since, 

 however, the data required for this can only be 

 obtained by visual observation, this light mea- 

 surer is not really independent of the human eye, 

 and therefore scarcely surmounts the colour 

 difiiculties experienced in ordinary photometric 

 measurements. 



Modern Mine Valuation. By M. Howard Burn- 

 ham. Pp. xi -I- 160. (London : Charles Griffin 

 and Co., Ltd., 1912.) Price los. 6d. net. 

 (Griffin's Mining Series.) 

 In this book the author discusses the fimdamentals 

 of mine valuation — a subject too seldom venti- 

 lated and too little introduced into the training 

 of mining engineers. 



The subject is treated mathematically. The 

 less secure an investment, the greater the interest 

 required ; the less an ore-body is disclosed, the 

 greater the insecurity and the greater the interest 

 demanded. According to the author, every occur- 

 rence of ore, whether it be but an outcrop un- 

 touched or whether it be an underground block 

 honeycombed with exposures, may, by the appli- 

 cation of a " risk rate " especially applicable to 

 it.=- condition, be valued mathematically and logic- 

 .ally. The descriptions of "positive," "probable," 

 and "possible," as applied to statements of ore- 

 reserve, disappear by this method ; each block 

 becomes rated at a present value corresponding 

 to the rate of interest demanded by its sufficiency 

 or insufficiency of exposure. Into this calcula- 

 tion, also, deferment is entered until the mathe- 

 matical formulae \v\\\ overwhelm the mining en- 

 gineer who took to mining under the idea that obser- 

 vation was the one important faculty to cultivate. 

 The procedure in calculating the results of 

 sampling is also carefully discussed, and towards 

 the end many useful tables of present values, at 

 various rates of interest, are given. Most of the 

 first portion of this book appeared in The Mining 

 Magazine late last vear, when its value was in- 

 creased by the discussion forthcoming from 

 various engineers. 



.'Mthough some of the views expressed and the 

 novel mathematical treatment may not command 

 entire agreement from his colleagues, the}' are 

 all assured that his work can only result in putting 

 the purchase and sale of mines upon a more logical 

 footing. .\ careful reading of this book, though 

 it mav be hard to many, will be of interest and 

 benefit to mining engineers generally, each of 

 whom, at some time or another, will find appli- 

 cation for some of the points elaborated. 



S. J- Truscott, 



