﻿390 Scientific Intelligence. 



Other measured angles are : 



Calculated. Measured. 



ct — 001 a 115 = 31° 6' 31° 9' 



C5=001 a 113=45° 10' 45° 9' 



cy = 001 a 112 = 56° 28' 56° 26' 



cp — 001 * 171 = 71° 40' 71° 40' 



SCIENTIFIC INTELLIGENCE. 



I. Chemistky and Physics. 



1. Geological Time. Address of Prof ess or G. H. Dakwin before 

 the Mathematical and Physical Section of the British Association 

 at Birmingham. — ... It will, I think, be useful to avail myself of 

 the present occasion to direct your attention to a certain group of 

 theories which are still in an undeveloped and somewhat discordant 

 condition, but which must form the nucleus round which many ob- 

 servations have yet to be collected before these theories and their 

 descendants can make a definitely accepted body of truth. If I 

 am disposed to criticise some of them in their actual form, I shall 

 not be understood as denying the great service which has been 

 rendered to science by their formulation. 



Great as have been the advances of geology during the pres- 

 ent century, we have no precise knowledge of one of its funda- 

 mental units. The scale of time on which we must suppose geo- 

 logical history to be drawn is important not only for geology 

 itself, but it has an intimate relation with some of the profoundest 

 questions of biology, physics, and cosmogony. 



We can hardly hope to obtain an accurate measure of time 

 from pure geology, for the extent to which the events chronicled 

 in strata were contemporaneous is not written in the strata them- 

 selves, and there are long intervals of time of which no record 

 has been preserved. 



An important step has been taken by Alfred Tylor, Croll, and 

 others, towards the determination of the rate of action of geolog- 

 ical agents. From estimates of the amount of sediment carried 

 down by rivers, it appears that it takes from 1000 to 6000 years to 

 remove one foot of rock from the general surface of a river basin. 



From a consideration of the denuding power of rivers and a 

 measurement of the thickness of stratified rock, Phillips has made 

 an estimate of the period of time comprised in geological history, 

 and finds that, from stratigraphical evidence alone, we may regard 

 the antiquity of life on the earth as being possibly between 38 

 and 96 millions of years ("Life on the Earth," Rede Lecture, 1860). 



Now while we should perhaps be wrong to pay much attention 

 to these figures, yet at least we gain some insight into the order 

 of magnitude of the periods with which we have to deal, and we 

 may feel confident that a million years is not an infinitesimal 

 fraction of the whole of geological time. 



