IV PREFACE. 



lication, and the Author hopes they will induce other artists 

 to devote their talents to this profitable branch of optical 

 science. In making this recommendation he is aware of 

 the feelings it will produce against him by some of the 

 present makers and their immediate patrons, but having no 

 interest of a private nature in these matters, it would ill 

 become him not to promote to the utmost his favorite 

 subject. 



" The importance of certain objects in determining the 

 qualities of Microscopes and Engiscopes is now duly 

 acknowledged; and as no complete account of these tests 

 at present exists, it is hoped that a full description of them 

 will be found useful; but to render the subject complete in 

 a scientific view, Dr. Goring has given a Memoir, ( On an 

 Exact Method of Ascertaining the Quality of Microscopes 

 and Engiscopes/ Of this method, which has hitherto 

 been a secret, its value may be somewhat appreciated when 

 it is stated that no perfect Achromatic Microscope has 

 been produced without it; and although they have been 

 known to the public some time, and profound mathemati- 

 cians have assiduously employed their talents in the inves- 

 tigation of the conditions necessary for obtaining Achroma- 

 tism and Aplanatism, yet no perfect instrument has been 

 produced, excepting by the means given in this Memoir. 

 The other Memoir by Dr. Goring, c On the Verification of 

 Microscopic Phenomena, 3 contains the sum and substance 

 of Microscopic Science. It is condensed into short apho- 

 risms, but I think will be found, on attentive perusal, to 

 contain all that is essential to a practical knowledge of the 

 subject." 



Canonbury Lane, Middlesex; 

 April, 1845. 



