BEYOND THE LIMITS OF VISION. 11 



perfectly inconceivable. The number of molecules in a cubic 

 inch of any gas at ordinary temperature and pressure is the 

 figure 3 followed by 20 ciphers. A drop of water contains about 

 the same number three hundred million million million. If 

 that little drop of water were magnified to a globe as large as 

 the whole earth, and its molecules were enlarged in the same 

 proportion, they would still be no larger than apples. Now you 

 may think of a pile of apples as large as a meeting-house, or a 

 hill, or possibly a mountain, but it is beyond all possibility to 

 realize the number that would be contained in a mass as large as 

 the world we live on. If Mount "Washington in the White 

 Mountains were all sand, there would not be as many grains in it 

 as there are molecules in a drop of water. 



The cheese-mite is a perfect little spider, with all the parts and 

 complicate organs of his order. This little insect, which you can 

 scarcely see by the naked eye, disposes of a number of structural 

 units represented by the figure 4 followed by 18 ciphers enough, 

 if they were the smallest beads you ever saw, and strung on a 

 thread that was long enough, to reach to the bright star Sirius. 

 If the body of an elephant were composed of only the same 

 number of particles enlarged that go to make up the smallest 

 living insect, the grained structure of the monster would still be 

 finer than the finest dust of wheaten flour. 



The smallest bacteria or infusoria, found so abundantly in foul 

 waters, and which can only be seen under the higher powers of 

 the microscope, are the proprietors each one of something like 

 four million million molecules. 



I have already mentioned the germs of the infusorium which 

 Dr. Dallinger saw under a magnification of five thousand diam- 

 eters as little clouds issuing from the cyst.* He tells us that he 

 once watched these clouds two weeks before they had increased in 

 size sufficiently for him to resolve them into discrete points as the 

 astronomer resolves the distant nebula into the faint glimmer of 

 separate stars ; both observations being on the extremest bounds 

 of the power of magnified vision. From this point of first 

 resolution, the germs gradually developed in about two days into 



Lecture before the British A. A. S., Montreal, 1884. 



