genuity has been exercised to produce an instrument by means of 

 which sketches of small objects can be made with the aid of the 

 microscope. The necessity for this class of work is very great. 

 The photographic camera does not materially assist us with most 

 subjects. Only in the case of exceedingly thin sections or natu- 

 ral objects of great thinness is a photomicrograph satisfactory. 

 In all other cases in order to fully elucidate the structure by 

 means of an illustration it is necessary to obtain the appearance 

 at different depths in the preparation. This can only be done by 

 focussing the microscope for each particular portion of the 

 structure. This fact, thus hastily explained, is what makes it 

 absolutely necessary to use a camera lucida for the proper rep-r 

 resentation of most microscopic objects. This fundamental 

 necessity is what has given rise to the many patterns which the 

 camera lucida has taken on during the course of its history. 

 The first instrument was an extremely simple one. From time 

 to time improvements and additions have been made until at 

 the present time the instruments issued by the best makers are 

 marvels of ingenuity and workmanship. In fact, in the writer's 

 opinion they are almost too ingenious, for it appears to him 

 that the various additions which have been made to the camera 

 lucida during recent years, while they do accomplish the object 

 aimed at, do so in an unsatisfactory manner. 



In order to produce a good camera lucida drawing, it is 

 necessary to have a certain degree of hght passing through 

 the microscope enabling the operator to see the object with the 

 greatest possible clearness. It next becomes necessary to so 

 modify the light from the drawing board as to enable him to see 

 his drawing point with the greatest possible clearness. Now, 

 with most objects it is not possible to secure this adjustment 

 once for all, for all portions of the drawing. Different portions 

 of the object emit different amounts of light, and, as the light 

 varies, it is necessary, in order that the drawing may be made 

 with the greatest precision and facility, that the light from the 

 drawing board should be modified accordingly. The accomplish- 

 ment of this end has been sought in a variety of ways, and this 

 more than any other one thing has added to the complexity of 

 the modern camera lucida. When the modern instrument is in 

 goocl order, it does, as we have admitted, in a way accomplish 

 Its object The difficulty is that it is easily thrown out of adjust- 

 ment, and easily becomes soiled and dusty so as to be a hind- 

 rance rather than a help. Again, no device has yet been furnish- 

 ed by manufacturers which enables one to modify the lieht ex- 

 cept by a series of steps. It is usual to insert or remove a cer- 

 tain number of tinted glasses until the right degree of light has 



