OF THE Mronosroi'K. I'.) 



its lower end to a transverse arm, which in turn is supported 

 by a stout bar, which is moved up and down by means of a 

 rack and pinion. This movement constitutes the coarse ad- 

 justment, the fine movement being effected by means of a lever 

 which is concealed in the transverse bar, and acts upon the 

 D one-piece. 



So far as mere questions of convenience and adaptability to 

 different kinds of work is concerned, this model is all that can 

 be desired, and as made by Boss & Co., the workmanship is so 

 perfect, and the finish so exquisite, that it has long maintained 

 a high position in public favor. It has, therefore, had numerous 

 imitators, and has probably been copied more extensively than 

 any other model in existence. At the recent Centennial Exhibi- 

 tion there were microscopes on this model from the most widely 

 scattered localities. Canada was represented by two micro- 

 scopes made after this design. Unfortunately, however, this 

 model is one of the very worst that a poor workman can 

 attempt to imitate, for unless the workmanship is far above the 

 average, the results are execrable. The reason for* (his is very 

 obvious. The body, being supported only at the lower end, 

 every vibration causes the upper end to swing through a com- 

 paratively large arc, and hence any motion arising from loose- 

 ness in the joints is multiplied a hundred fold. . And even when 

 the joints are firm and without shake, any vibration communi- 

 cated to the table on which the instrument stands, is greatly 

 increased in its effects when it reaches the upper end of 

 the body. In addition to this, the unsupported part of the 

 body acquires, by each movement, a momentum which reacts 

 powerfully on the lower part, and consequently on the ob- 

 jective. 



These defects have induced Messrs. Boss & Co. to bring out 

 a new pattern designed after the Jackson model. This design 

 has been carefully worked out by Mr. Wenham, and is certainly 

 very beautiful in appearance, and very efficient and convenient 

 in use. Our readers will therefore bear in mind, that all micro- 

 scopes made by Boss & Co., are not made on the "Boss 

 model," 



