OF THE MICROSCOPE. ' 61 



OBJECTIVES. 



The modern compound microscope owes almost all its value 

 to the high degree of perfection which has been attained in the 

 construction of the objectives used with it. Some of the old 

 microscope stands were quite as elaborate, and quite as costly, 

 as anything that can be found in the workshops of our modern 

 opticians, but from the fact that the objectives were defective, 

 their value as instruments of research was of a very low degree. 

 In these old microscopes even the highest power objectives were 

 simply bits of ground glass, such as with our modern appliances 

 might easily be produced for ten cents apiece, while a modern 

 objective of the same power, by any of our first-class makers, 

 would cost at least one hundred dollai's. In mechanical exe- 

 cution the modern objective approaches more nearly to theo- 

 retical perfection than any other instrument made by man, but 

 the reader must not infer from this, as some have done, that 

 it has reached the limit of perfection, and that nothing more 

 is to be expected. This was said ten, twenty, and thirty years 

 ago, and in each case the words had hardly been committed 

 to paper before some optician proved their falsity by accom- 

 plishing that which had just been declared to be impossible ! 

 Within the past few years the most wonderful improvements 

 have been effected, and from present indications it would seem 

 that we are on the eve of still more startling developments. 



Since, then, the objective is really the most important part of 

 every microscope, seeing that the quality and trustworthiness 

 of the work done must depend to a very great extent upon its 

 efficiency, it is of some importance to the microscopist that he 

 should have at least a fair understanding of the causes to which 

 the superiority of modern objectives is due. 



When we use a simple glass lens as an objective for a com- 

 pound microscope, we find, on attempting to examine objects 

 under powers of more than one hundred diameters, the following 

 defects and difficulties : The field of view is so dimly illuminated 

 that objects are seen with difficulty ; the outlines of the different 

 parts, instead of being sharp and clear, are thick and hazy : 

 several of the lines are fringed with brilliant colors, but colors. 



