256 Notices of Books. [April, 



ments, or other supports for girders, and are most important. 

 The tensile strength of materials is very fully discussed, and is 

 followed by chapters on Shearing-Strains, Elasticity and Set, 

 and Temperature. Next follow chapters on the detail parts of 

 girders and bridges, such as flanges, web, cross-girders and 

 platform, working load, &c. ; after which several pages are given 

 to estimation of girder work, which forms a most fitting sequel 

 to what has preceded. The book concludes with an appendix, in 

 which many interesting and detailed particulars are given of the 

 Boyne Lattice Bridge, on the Dublin and Belfast Junction Rail- 

 way, which affords a practical illustration of the theories laid 

 down in the main body of the book. 



On the Cause, Date, and Duration of the Last Glacial Epoch of 

 Geology, and the Probable Antiquity of Man. With an Inves- 

 tigation and Description of a New Movement of the Earth. 

 By Lieut.-Col. Drayson, R.A., F.R.A.S., &c. London : 

 Chapman and Hall. 1873. 



In spite of all that has been written — whether by geologist, as- 

 tronomer, or physicist — in explanation of the different conditions 

 of climate in past phases of the earth's history, the subject still 

 remains so enshrouded in obscurity that light from any quarter 

 should be gladly greeted. Perhaps the most remarkable — cer- 

 tainly the most interesting — of these climatic conditions is repre- 

 sented by that period which geologists recognise as the Glacial 

 Epoch, — an epoch in which arctic conditions seem to have pre- 

 vailed over the northern hemisphere down to at least the forty- 

 fifth parallel of latitude. It is universally conceded that this 

 episode in the history of our planet occurred in comparatively 

 recent geological times, but we are as ignorant of its absolute 

 date and period of duration as of the physical causes by which 

 it was brought about. It is, however, to the solution of these 

 problems that Col. Drayson addresses himself in the present 

 work. 



Rather than offer his own description of the Glacial Epoch, 

 the author cites copiously from the writings of Ramsay, Lyell, 

 Agassiz, Page, and other geologists. He then discusses and 

 dismisses the several theories which have from time to time 

 been advanced with the view of explaining the cause of these 

 glacial conditions, — such as the passages of the earth, with the 

 rest of the solar system, through zones of space of different 

 temperatures; the assumed changes in the excentricity of the 

 earth's orbit ; differences in the distribution of the great masses 

 of land and water; and alteration in the position of the earth's 

 poles by shifting of the axis. It is strange that we fail to find 

 here any reference to the writings of Mr. Croll, who has, of late 

 years, so ably discussed some of these theories. 



