154 Transactions of the Royal Microscopical Society. 



used as a condenser being capable of forming a test-image, wbich 

 at once declares, like a telescopic test, its conditions beyond any- 

 possible doubt : because its appearance when magnified up can at 

 once be compared with the tangible reality as it appears to the eye 

 of the observer. In each case it is advisable to magnify the minia- 

 ture so as to appear as large as the real object. This is a totally 

 different thing from a disputed scale of an insect which we cannot 

 see with the naked eye. 



