2 4 8 



NA TURE 



[January i i, 1906 



is to be his course of study in between ? Before the 

 advanced treatise, or, at any rate, such a one as Dr. 

 Marr would approve, can be really entered on and 

 appreciated, the student must surely have some prac- 

 tical acquaintance with carbon dioxide and silica as 

 chemical substances, with " boneless animals " and 

 "those possessing bones," and with other matters 

 that are here mentioned as if they were absolutely 

 new to his intelligence. On pp. 224 and 225 the 

 beginner is sent out into the open country as his 

 "true museum." This is excellent advice for the 

 true beginner in geology, but not for those beginners 

 in science whom Dr. Marr, from his experience of 

 English public schools, finds himself compelled to 

 contemplate. 



Among the excellent points in the present treatise 

 we notice the early introduction of conceptions of 

 crust-movement, which render descriptions of other 

 phenomena far more easy of comprehension; the 

 reference to what is often known as " plucking " in 



the action of glaciers (p. 57) ; and the concise account 

 of plains of denudation (peneplains) on p. 99. Among 

 the very few slips, we may note that Kimeridge (p. 

 179) is in Dorset, not in Wiltshire; that the insoluble 

 part of felspar (p. 79) does not by itself form china- 

 1 l.i\ ; and that the phrase " evaporation of water by 

 the sun " (p. 07) is scarcely a happy one. The fan- 

 structure on p. 93 is, we think, not that usually 

 thought of in connection with the term. 



On p. 65 we must invoke subsidence of the crust to 

 enable the sea to perform all the work there claimed 

 lor it; and we should like more sympathy on p. So 

 with the view that the earth is continually losing 

 moisture from its interior. Lastly, the author (p. 181) 

 should not, even by an accident of phraseology, en- 

 courage .1 belief in the existence of "fossil thunder- 

 bolts." But these small asperities only give an edge 

 io our appreciation. Grenville A. J. Cole. 



NO. 1889, VOL. 73] 



TIDAL RESEARCHES. 1 



ONE of the crowning features of the enunciation 

 by Newton of the law of universal gravitation 

 consisted in the fact that herein the phenomena of 

 the tides and their relationship with the moon could 

 for the first time be coordinated with other well- 

 known phenomena of the solar system. Though the 

 principal phenomena of rise and fall and ebb and 

 flood of the sea must have been recognised bv coast 

 dwellers and navigators from the earliest times, the 

 theory of the tides as it exists to-day may fairly be 

 said to have originated with Newton, and its purpose 

 lias largely been to examine to what extent these 

 phenomena are attributable solely to a gravitational 

 cause or how far it may be necessary to invoke some 

 other exciting or controlling influence. 



ll was early recognised that a theory which failed 

 to take due account of the inertia of the water, of the 

 earth's rotation, and of the curvature of its surface 

 could but i n- 

 adequately repre- 

 sent the phe- 

 nomena actually 

 existent in nature, 

 and the reduction 

 of the tidal pro- 

 blem to a mathe- 

 matical form in 

 which all these 

 features were duly 

 taken into account 

 was first accom- 

 plished by Lap- 

 lace ; since his 

 time the equations 

 furnished by him 

 have formed the 

 basis of almost all 

 attempts to fur- 

 ther the study of 

 the tides from its 

 purely theoretical 

 aspect. The 

 theory of tides in 

 narrow canals de- 

 veloped in extenso 

 by Airy, though 

 not directly based 

 on Laplace's 

 equations, con- 

 sists largely in 

 the discussion of 

 a special type of 

 solvable cases of 

 the more general mathematical "problem pro- 

 pounded by Laplace. In the memoirs under re- 

 view the author emphasises the hopelessness 

 of such attempts to realise their main purpose of 

 providing a theory sufficiently exact and yet sum- 

 iienil\ general in character to allow of direct com- 

 parison with observations, as is the practice in the 

 study of other gravitational phenomena such as the 

 planetary motions, and proposes a new method of 

 attacking the problem. An essential difference between 

 this method and that of Laplace consists in the fact 

 that in the former the influence of the earth's rota- 

 tion is regarded as of secondary importance. Such 

 solutions of Laplace's equations as have been 

 obtained, which allow of an exact estimate of the 



1 "A Manual of Tides." Partiv. A, Outlines of Tidal Theory. Part iv. B, 

 Cotidal Lines of the World. By Rollin A. Harris. Appendices to Reports 

 of U.S. Coast and Geodetic Survey. 



ival ot New Red Sandstone, Ch 

 troduction to Geology.") 



Forest. 



