NOTES AND COREESPONDENCE. 



New Method of Fixing the Objective. — We have received the 

 following from Professor Claparede, of Geneva. — " I am 

 anxious to recommend to all savants or amateurs who occupy 

 themselves with the microscope a very convenient addition 

 due to the invention of Professor Thury, engineer of the 

 Genevese Society for the Construction of Physical In- 

 struments, and employed by the same Society in the con- 

 struction of its excellent compound microscopes. This ad- 

 dition consists of a spring clip, which is fixed at the extremity 

 of the tube to which the objective is screwed. This clip bas 

 a part turned in steel, with the greatest care, under which 

 it is only necessary to slide the objective, which can be thus 

 easily put on and taken off instantaneously. For this pur- 

 pose a small intermediate piece is screwed on to the objective, 

 which is made to fit exactly into the clip. 



" This invention, which is very much to be preferred to the 

 so-called revolving system, presents besides the advantage of 

 a great economy of time in changing the objective, that of 

 permitting a more exact meclianical centering of the objec- 

 tive — than that which one could obtain by the screw ; and 

 it also allows the employment in the observation of an object, 

 of that part of the objective which gives the best images. 

 This system can be adapted directly to all microscopes pro- 

 vided with the English screw, and by the modification of the 

 intermediate piece as required, can be adapted to the ob- 

 jectives of all the principal English, French, and German 

 makers." 



English versus French Objectives. — One of the editors of 

 this Journal has now had considerable experience of the ob- 

 jectives of Hartnack, of Paris, and his pupil, Yerick, the 

 former of the Place Dauphine, the latter of 2, Rue de la Par- 

 cheminncrie, Paris, and he is anxious that all wlio use the 

 microscope should know of the excellence and cheapness of 

 these makers' glasses. At Vienna, in the laboratories of Roki- 

 tansky and Strieker, the glasses of Hartnack are alone used, 

 and their excellence well prov(!(I by the work done : they are 

 also in use in most of the Gei-man laboratories. Hartnack's 



