174 Analysis of Scientific Books and Memoirs. 



. + 0."72; the entire rate for the whole period being ■+• 20."4, or an incre- 

 ment to its detached rate of 18. "5. 



The succeeding day, the two Chronometers were restored to the full 

 pressure of the atmosphere ; and the first hour after their restoration, an 

 attempt was made to discover the same increments as existed under the 

 receiver, but without effect ; the rate for the entire twenty-four hours of 

 the pocket Chronometer being + 10."08, and of the other + l."0. Hence, 

 Mr Harvey infers, that the change produced in the rate of a Chronometer 

 by diminishing the density of the air, is immediate and uniform in its ef- 

 fects ; and so also is the effect produced by increasing it. 



We confess we thought, when considering the remarkable differences of 

 density to which the chronometers were subjected during these experi- 

 ments, that considerable derangements must result to their ordinary rates ; 

 but we were happy to observe that Mr Harvey has furnished many exam- 

 ples, illustrative of the power which most time-keepers possess, of regain- 

 ing their original rates, or very nearly so, after they have been subjected 

 to pressures, both considerably above and below the mean density of the 

 air. Mr Harvey furnishes one most remarkable example of a chronome- 

 ter, which possessed the power of immediately altering its rate with every 

 new circumstance in which it was placed, and also of regaining its origi- 

 nal rate, after being again restored to its primitive condition. During the 

 course of observations, and which embraced a period of four months, this 

 time-keeper was subjected to pressures from 60 inches to 3 inches, and the 

 power it possessed of regaining its original rate, may be observed in the 

 next table. 



During the investigation, Mr Harvey attended to the changes of tempe- 

 rature, always accompanying sudden alterations in the density of the air ; 

 and, following the opinion of Mr Dalton, that it is the effect of a degree 

 of heat amounting probably to 40 or 50 degrees, yet only allowed to exer- 

 cise its influence for a few seconds, in consequence of the immediate effort 

 made by the receiver and the surrounding objects, to restore the primitive 

 temperature, the effect on a delicate thermometer is only that of two or 

 three degrees. Hence Mr Harvey introduced a very susceptible time- 

 keeper, into an atmosphere 50° warmer than the ordinary state of the air 

 for ten seconds, but found no alteration of rate to result from it. 



In accounting for these curious and singular alterations of rate, Mr 

 Harvey availed himself of the admirable paper of Mr Atwood, contained 

 in the Philosophical Transactions for 1794, and by an extension of that 

 very learned philosopher's formula for representing the daily aberration of a 



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