CHAP. XIX. EVIDENCES OF HABITUATION. 373 



the rates. Few of these examples can properly be compared with 

 each other ; for, besides the reason given upon p. 299, on some 

 occasions the party was larger or smaller (and this always exerts 

 an influence) ; and sometimes we were laden and at others unen- 

 cumbered. The condition of the weather has also to be taken into 

 account. 



Upon the whole these observations afford indications that we 

 became someichat habituated to low pressures. If the entries at 

 January 3, 6 and 7 are compared, a continuous advance will be 

 noted. This, however, was partly due to increasing familiarity 

 with the ground which was traversed. There is stronger evidence 

 of improvement on Feb. 18, when over a much longer course the 

 mean rate was faster than on the shorter one of January 3 ; and 

 this was exceeded upon March 10 and April 4 when we were 

 unembarrassed by natives. The nature of the work upon Illiniza 

 and Cotocachi was similar, and through absorption of time by step- 

 cutting the rates upon those mountains were slower than upon 

 Ootopaxi, Antisana or Cayambe. Comparison of the entries at 

 Feb. 9, April 24 and June 9 shews no deterioration, although there 

 is little sign of progress. There is a more marked contrast between 

 the rates of January 4 and July 3, but this is modified if due 

 allowance is made in the first case for the exceptional softness 

 of the snow, in the second one for the greater simplicity of the 

 route. 



But although it seemed that we did become somewhat habitu- 

 ated to low pressures, and that this was shewn amongst other 

 ways by improvement in speed, it appeared to me that the best of 

 our rates were inferior to those which we should have attained 

 over the same ground at higher pressures ; and I brought this 

 point to the test related upon pp. 300-301, and obtained from 

 that experiment evidence that I was materially affected by, and 

 weakened at, a pressure of 21 inches (9850 feet). It need scarcely 

 be remarked that this observation has a very wide interest ; for, 

 if it is really the case that the bodily powers are lessened under 



