Geology. 403 



-which is largely free from the sources of error which vitiated 

 the earlier work. The new system consists essentially of a cube 

 of crown glass suitably suspended by a brass rod and a quartz 

 fiber. The cube was made as perfect as possible and, when 

 suspended, four of its edges were vertical and parallel to the axis 

 of rotation. The horizontal beam of light passed diagonally 

 through the cube and experienced two refractions and only two 

 primary reflections. The suspended system was enclosed in a 

 gun-metal box which was fitted with the necessary lateral tubes, 

 windows, etc. 



Details of the precautions taken with respect to " gas action " 

 and convection currents may be omitted in this place. Also, the 

 calculations of the torque, of the reflection corrections, and of the 

 energy density of the beam of light afford no novelty. It is worthy 

 of note, however, that Barlow found hydrogen far more reliable 

 than air inside of the box enclosing the suspended system. The 

 calculated and observed deflections agree as well as can be 

 expected when the inherent difficulties of the experiments are 

 given due consideration. The observed deflections are systemat- 

 ically larger than the calculated deflections, which shows either 

 that some source of error has been overlooked or that a funda- 

 mental datum was not determined with sufficient accuracy. 

 Nevertheless the following statement of the author seems justified 

 by the final results, namely : " We may therefore conclude that 

 the oblique passage of a beam of light through a plate of refract- 

 ing material produces on the matter of the plate a torque which 

 has the magnitude deduced from the transfer of momentum in 

 the beam." — Proc. Roy. Soc, vol. lxxxvii, No. A 592, p. 1. 



h. s. u. 



II. Geology. 



1. Sub -Oceanic Physiography of the North Atlantic Ocean; 

 by Prof. Edward Hull. Atlas with eleven folio maps in color. 

 London (Edward Stanford). — The maps here given show in 

 better form than anything previously published, the borders of the 

 continental platforms, indented by valleys and embayments, and 

 further crossed by great river-like valleys and canyons, extending 

 from the present continental rivers, such as the Hudson channel, 

 as first noticed by Professor J. D. Dana ; and later built up into 

 systems by Spencer, Hull, and Nansen, in order of time. Hull's 

 charts show the indented 'borders of the Eastern Continents, like 

 those of high plateau regions, and also many submerged river- 

 valleys, such as those of the English Channel River, Irish Sea 

 River, the canyons of the Adour and Tagus, of the Congo, and 

 others in the Mediterranean ; while in a condensed form, the 

 numerous submarine valley-systems off the American coast, as 

 developed by the reviewer, are added, thus making the subject more 

 complete. Hull is led to conclude that these high plateaus were 

 the courses of former land valleys, and accordingly in them are 

 found means of measuring the late changes of land and sea. 

 The former high elevations and continental extensions are sup- 

 ported by the distribution of animals and plants, and late glacial 



