1871.] Notices of Books. 379 



Iron and Heat. By James Armour, C.E. London: Lockwood 

 and Co. 163 pp. 



This manual may be divided into two sections. The first 

 comprises the fundamental principles concerned in the con- 

 struction of iron beams, pillars, and bridge girders ; the second 

 deals with the action of heat upon the different materials of iron- 

 smelting. The language is simple, and the mathematical 

 illustrations in the first part of the work, as well as the definition 

 of the laws of chemical combination concerned in the second, 

 are such as will be readily understood by the practical workman. 

 The use of logarithms in calculating strains by Hodgkinson's 

 formulas is shown with great clearness and brevity, while with 

 equal terseness the combinations taking place chemically in the 

 interior of the furnace during the smelting of the iron are 

 explained by measure instead of by the atomic theory. Mr. 

 Armour will no doubt find many readers among the practical 

 men for whom he writes, and with whom his own experience 

 will have its weight. 



Fragments of Science for Unscientific People. By John Tyndall, 

 LL.D., F.R.S. London: Longmans, Green, and Co. 



These fragments are in reality solid intellectual repasts provided 

 at different times for large audiences ; but the illustrations are so 

 fresh that the repetition consequent upon the aggregation of 

 articles written on the same subject for distinct purposes does 

 not cloy. The first essay is a very happy exposition of its title, 

 " The Constitution of Nature." It presents to the unscientific 

 reader the most important physical laws, pictured in that lucid 

 manner which the author advises as the only successful method 

 of study. Perhaps no other writer has been able to make the 

 conception of an interstellar medium so comprehensible to the 

 student. The present theory of Heat and Light is easily enough 

 understood, once the imagination has accepted the existence of 

 an interstellar luminiferous aether ; but it is this endeavour to 

 grasp the intangible that appears the stumbling-block of the tyro 

 in science. How Dr. Tyndall makes this the starting-point 

 from which he tends to the consideration of an extra-aetherial 

 sun is best told in his own words. 



" Imagine a paddle-wheel placed in water and caused to 

 rotate. From it as a centre, waves would issue in all directions, 

 and a wader as he approached the place of disturbance would be 

 met by stronger and stronger waves. This gradual augmentation 

 of the impressions made upon the wader's body is exactly 

 analogous to the augmentation of light when we approach a 

 luminous source. In the one case, however, the coarse common 

 nerves of the body suffice ; for the other we must have the finer 



