ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



119 



With this device both, hands must be used either in attaching or 

 removing the objective, and no provision is made to insure accuracy 

 of centering. In the apparatus from which the above description was 



Fig. 16. Fig. 17, 



made the objective had a lateral 

 play at the shoulder of about 

 1/50 in. when the collar was se- 

 cured with moderate force. Such 

 loose fitting would be found very 

 inconvenient in the registration 

 of the positions of small objects 

 with high powers. Altogether, we cannot but think that the appa- 

 ratus is more complicated than is at all necessary. Whilst it has 

 the studs of Nelson's form it lacks the simplicity of the turn of the 

 objective with the same hand that holds it, and whilst it has_ the 

 rotating collar of the Watson-Matthews form (amply sufficient to hold 

 the objective) it has the additional complication of studs in place of 

 a simple conical fitting. 



Abbe's Camera Lucida.*— G. Kohl gives the annexed fig., 18, of 



Fig. 18. 



what he terms " Boecker's new drawing apparatus after Dippel," but 

 which is in reality Professor Abbe's Camera Lucida.t 



* Bot. Centralbl., xvi. (1883) pp. 385-6 (1 fig.), 

 t See this Journal, iii. (1883) p. 278. 



