4 88 THE POPULAR SCIENCE MONTHLY. 



plished by physical astronomy. Is it not enough, however, to show 

 that our branch of the science has already attained the height of its 

 elder sister ? Are not the two worthy of each other, and will they 

 not be able to march hereafter at an equal pace to the conquest of the 

 heavens ? On one side we behold the calculus that marvelous intel- 

 lectual lever, putting the data of observation to work, and drawing 

 from them magnificent and unexpected consequences. On the other 

 side, that wonderful apparatus which analyzes light as if it were mat- 

 ter, which forces it to give images of near and distant objects alike, 

 and, seizing the fugitive images, makes them fixed and durable. 



Behold on one side, again, the mathematical genius that has cre- 

 ated the analysis of the infinite, a genius of exactness and thorough- 

 ness, which is able to enter into all the elements of a question and 

 disengage from the complication of data the ultimate consequences 

 signified by them. On the other side, the genius of observation, 

 which now watches phenomena with the innate and superior sense 

 that enables it to discover their intimate relations, now questions Nat- 

 ure and carries on its experiments as the geometrician carries on his 

 analysis when he wishes to prove or discover something, and now, 

 illuminated by a sudden inspiration, makes at a stroke one of those 

 approaches that open immense horizons. 



On one side behold, finally, the heavens measured, the solar world 

 placed in the balance, and its movements so well linked together by 

 the law that governs them that soon, perhaps, past, present, and fut- 

 ure will no longer exist for astronomy. On the other side, wonders 

 still more astonishing : stars revealing to us their forms and the most 

 minute details of their structure, as if they had left the depths of 

 space to offer themselves submissively to our study ; worlds intrust- 

 ing the secrets of the matter that engenders them to the rays which 

 they send us ; and the history of the sky written by the sky itself. 

 Finally, by the united efforts of the two, the entire universe, in its 

 majesty and its grandeur, become the intellectual domain of man. 



-- 



EVOLUTION OF THE STETHOSCOPE. 



By SAMUEL WELKS, M. D., F. E. S., 



PIIYSICIAN AND LECTURER ON MEDICINE, GL'T's HOSPITAL. 



INSTEAD of placing on the table every imaginary form of stetho- 

 scope manufactured out of every possible material gathered from 

 the shops of the instrument-makers, I will carry you back to the 

 origin of the stethoscope, and you will see how, on the principle of 

 selection and the survival of the fittest, the primitive instruments have 

 departed from the scene and are now only to be found among the 



