CHAPTER III. 



TEST OBJECTS. 



This important class of bodies — ^the properties of which 

 were discovered by the late Dr. Goring — deserve special 

 notice. It will therefore best serve the purpose of the 

 Microscopist to insert here Mr. Pritchard's essay on this 

 subject, as the "Microscopic Cabinet," in which it originally 

 appeared, is out of print. To that essay will be added 

 such discoveries as have been made subsequent to its 

 publication. 



" Every important advance in our knowledge of those 

 bodies in the material universe from which our earth 

 appears as an atom, has been coeval with and greatly 

 dependent upon some augmentation of the powers and 

 effectiveness of telescopes. Before the discovery of the 

 double stars and nebulae, the goodness of these instru- 

 ments was determined by their capability of showing the 

 planets and their satellites. But since our acquaintance 

 with the former bodies, telescopes have to "undergo more 

 severe tests, and greater accuracy in their construction is 

 required. What has been advanced in regard to the tele- 

 scope will be found also applicable to the microscope ; and 

 to the discovery of certain objects which may be considered 



