THE 



POPULAR SCIENCE 

 MONTHLY. 



AUGUST, 1874. 



PEIESTLEY'S DISCOYERY OF OXYGEN GAS/ 



By JOHN WILLIAM DRAPEE, M.D., LL. D. 



ANIMAL instincts, when properly considered, are often found to 

 be connected with physical laws. Even in the case of man, his 

 gratifications and dislikes frequently originate in the imperceptible 

 action of external circumstances, and those feelings, and the impulses 

 to which they give rise, are, in the scheme of Nature, strangely bound 

 up with other things, with which, at first sight, they seem to have no 

 kind of connection. 



Thus, with what pleasure the whole animal world rejoices at the 

 coming of spring ! There is a heart-felt delight, not limited to the 

 higher races, but common to all. With the returning temperature, 

 birds, and beasts, and insects, prepare for the duties of a new year, 

 and every thing seems full of animation and life. Even the illiterate 

 man cannot look unmoved on the green tint stealing over the fields. 

 Perhaps his sentiments may in some measure be connected with a per- 

 ception that there is a promise for the gratification of his baser ani- 

 mal appetites, and that this prosperous beginning will end in the pro- 

 duction of corn and wine for his use. But, behind these, which are 

 the more obvious, there are other causes for rejoicing — causes which 

 can only be fully appreciated by the intelligent, and which have been 

 made plain only by the advances of the highest branches of human 

 knowledge. 



How often is our admiration aroused by the work of mechanical 

 artists ! — the steamship, which day after day has continued its unceas- 

 ing and successful struggles with the waves, or the chronometer, which, 

 once wound up, keeps on for months together its regulated motion. 

 Yet how far are all these contrivances outdone in the mechanism of 

 every living man ! Of his double nervous system, one part, the intellect- 

 ual, observes its mysterious periodicities, its time of activity and time 



^ A Lecture ; see Sketch of Priestley in present number. 

 VOL. V. — 25 



