STOMATA AND DROUGHT RESISTANCE IN MEALIES. 185 



As, however, the present paper deals only with the consideration of 

 the stomata, 1 have left the investigation of these ahsorhing celU 

 for another later occasion. 



Electrical Illumination. — Of Messrs. C. Griffin 

 & Co.'s series of scientific and technical works, probably those 

 dealing with chemical and metallurgical subjects are the best 

 known in South Africa. Prof. H. l>ohle, of the South African 

 College, has recently, and by no means for the first time, con- 

 tributed to that excellent series a book dealing with electro- 

 technics. Its title is " Electro-photometry and Illumination,"* 

 and it is primarily intended as a text-book for second-year engi- 

 neering students. It contains, in an amplified form, the lectures 

 delivered by the author during 191 1. A great many of the tests 

 described were carried out in the laboratory of the South 

 African College, and in this book they appear for the first time. 

 Although the book is intended primarily for college students, 

 others interested in illuminating engineering, such as medical 

 men, architects, teachers, and even the general public, will find 

 it useful. The first three chapters are mainly occupied with 

 photometry ; the principles on which photometric measurements 

 depend are explained and the most important light-standards 

 described. Then radiation and its effects claim attention, special 

 reference being made to the physiological action of the ultra- 

 violet rays, as well as to their germicidal properties, and, in this 

 connection, to their commercial application for purifying water. 

 Full description is given of various kinds of photometric 

 apparatus and of the appliances needed for the equipment of a 

 photometer room. After a chapter devoted to light flux and 

 distribution, the author passes on to deal with electric lamp test- 

 ing, incidentally discussing the question whether our lamps are 

 run with the most economical efficiency, showing how this may 

 be determined, and under what circumstances commercially 

 better results may be obtained. A good deal of consideration 

 is given to the designing of reflectors and shades, and the remark 

 is made that opal and frosted globes absorb a considerable 

 amount of light, and that prismatic, or " holophane " shades and 

 reflectors produce better results. The closing chapter of the 

 book deals with illuminating engineering. The illuminating 

 engineer has to satisfy two requirements simultaneously : those 

 of physics and of physiology. He should therefore be careful 

 not to neglect one at the expense of the other. Here colour and 

 uniformity of illumination are of great importance. Sugges- 

 tions are made for the lighting of private houses and different 

 classes of public and semi-public places, and several illustrative 

 examples of illuminating engineering are given, including the 

 library and assembly room of the Hiddingh Hall, South African 

 College. A lengthy bibliography of chief publications subse- 

 quent to 1906 is appended to the book. 



* Large 8vo. pp. xii, 222. ]0s, 6d, nett. 



