March 26, 1903] 



NA TURE 



483 



and soil are discussed in another chapter, but more 

 detail is required regarding- the latter. 



The chief part of the book (pp. 38-532) describes the 

 forest species, and is done much in the same way as 

 by Mathieu in " La Flore Forestiere," with the addition 

 of some sylvicultural details. It differs, however, from 

 the latter by the addition of ninety-two excellent 

 botanical plates, showing the structure of the branches, 

 foliage, flowers, fruit and wood of the principal species. 



The exotic species described are few in number, and 

 most of them are without sylvicultural importance, 

 except in Algiers and Corsica, where species of Euca- 

 lyptus, GrcviUca robusta and Casaarina tennissima 

 thrive. Of the few exotic broad-leaved trees which 

 thrive in temperate districts, Liriodendron Utlipifera, 

 the wood of which from America, combining the quali- 

 ties of lime, alder and poplar, is largely used in France, 

 Juglans nigra and Carya alba deserve notice. Among 

 conifers, the Douglas fir, Menzies spruce and Thuya 

 gigantea may be mentioned, Weymouth pine having 

 been long naturalised, and figuring among the in- 

 digenous species. 



This is a valuable book, but its value would have 

 been enhanced had there been more sylvicultural detail. 

 The remaining three volumes will be awaited with 

 interest. W. R. Fisher. 



THE ART OF ILLUMINATION. 

 The Art of Illumination. By Louis Bell, Ph.D. 



Pp. ix + 345 ; with 127 illustrations. (New York : 



McGraw Publishing Co., 1902.) Price 2.50 dollars. 

 Al^HEN the importance of artificial light and its 



* * effect upon our comfort and eyes is con- 

 sidered, it seems impossible that the technique of 

 healthy and satisfactory lighting should have been 

 neglected in the way it has. The fact, however, re- 

 mains that although there are books in plenty on the 

 various available illuminants and the generation of 

 light from them, yet the true art of illumination has 

 received but scant attention. 



Dr. Louis Bell, in attacking this important pro- 

 blem, has done well in devoting the first three 

 chapters of his book to the effect of light and colour 

 on the eye, and the works of Chevreul, Helmholtz 

 and Abney are effectively laid under contribution to 

 provide a firm foundation for the latter part of the 

 work. The effect of faulty and flickering illumination 

 upon the eye, and the damage to the eyesight brought 

 about by excessive and unshaded lights, is dealt with, 

 but it cannot be too strongly insisted upon that we 

 are living in an age of intemperance with regard to 

 artificial light that is likely, after a few generations, 

 to produce serious racial eye trouble. Already we 

 cannot work with comfort by the light that served 

 our fathers, and although a certain advance in 

 quantity of light was an advantage as saving strain 

 upon the eyes, yet there is no doubt that the present 

 tendency to high-power incandescent and arc lights 

 is not only inartistic, but harmful, as the small area 

 from which the light is emitted and the high in- 

 tensity throw a serious strain upon the eye, and yet 

 the light given has but little diffusive power. 

 NO 1743, VOL. 67] 



Chapters iv. and v., which deal with combustible 

 illuminants and incandescent mantles, are the least 

 satisfactory in the book, this being partly due to the 

 fact that the conditions of cost here and in America 

 are so different, and largely also to the evident fact 

 that Dr. Bell is more at home with electric than with 

 combustible illuminants. 



When one finds it freely stated that " incandescent 

 electric lamps are about equivalent to ordinary gas in 

 cost, with a tremendous hygienic advantage in their 

 favour," it must be remembered that the cost of the 

 gas is 1 to 1.50 dollars per 1000 cubic feet, and that 

 an electrician always overlooks the fact that the hot 

 products of combustion from a gas flame are among 

 the most powerful factors in ordinary ventilation. 

 In Fig. 21, a Siemens regenerative burner is figured 

 as a Wenham, whilst the Wenham is shown at Fig. 

 22 as a Siemens. Full justice is done to acetylene, 

 but the author shows but little knowledge of the in- 

 candescent mantle when he speaks of it in one place 

 as being composed of various blends of the more 

 accessible of the rare earths and in another says it 

 is " well known to consist essentially of the oxides 

 of the so-called metals of the rare earths, chiefly 

 thorium and yttrium." The data given as to the 

 candle-power and life of the mantle also suggest 

 that this part of the subject has not been quite 

 brought up to date. 



In the chapter on incandescent mantle lighting for 

 open spaces, no mention is made of such high-candle- 

 power units as are now given by the high-pressure gas 

 systems and the Kitson (oil) burners; indeed, a mantle 

 giving 100 candle-power is spoken of as somewhat ex- 

 ceptional, whilst in Berlin at the present time there are 

 plenty of mantles giving 1500 candle-power with gas at 

 a water pressure of 4J feet. 



Passing on to the chapters on electric lighting, one 

 has nothing but praise; the author knows his work 

 thoroughly, and a better popular treatise on the sub- 

 ject would be hard to find, whilst undoubtedly the 

 best portion of the whole book is that dealing with 

 the title matter — the art of illumination. 



At the present time everything is being done that 

 can be done to increase the intensity of local centres 

 of light, a condition of things brought about by the 

 advent of the electric arc for outdoor illumination, 

 and the feeling that if gas or other illuminants are 

 to hold their own for this purpose, they must be able 

 to complete in this respect. 



This, however, is an advance on totally wrong lines, 

 and the author has done good service to the art of 

 illumination by pointing out that its progress must 

 always be in more and more complete subdivision of 

 the illuminating radiants, and the subordination of 

 great brilliancy to perfect distribution. 



The concluding chapter deals with standards of 

 light, and gives full credit to Mr. Vernon Harcourt's 

 10-candle pentane lamp as a trustworthy and repro- 

 ducible standard. 



Everyone interested in the present phases of street 

 illumination will read with pleasure the remarks made 

 by the author on the nominal rafing of the candle- 

 power of electric arc lamps, which " have long since 



