Stoddor.] 338 [December 11, 



stru}), who had observed the same tiling in Denmark, sus- 

 pected that the bones liad been mutihited l)y animals ; upon 

 experiment, he found that dogs eat the ends of the bones of 

 birds an<l reject the shafts. Most of the snails wci-e minute 

 and only incidentally present. 



The President announced Ihat the Society was about to 

 resume its former, plan of giving public lectures on Natural 

 History. The first series would consist of a course of six 

 lectures on Mollusca, by Mr. E. S. Morse, the Curator of 

 Conchology. The lectures would be given on successive 

 Saturdays at 3, P.M., commencing December 7. Owing to 

 the small size of the lecture room a regulation price of one 

 dollar for the course would be charged. 



Section of Microscopy. December 11, 1867. 

 The Curator in the chair. Seven members present. 

 The following paper was read : — 



Nobert's Test. By Charles Stoddeu. 



Most microscopists know the value of "Nobert's test" for ascertain- 

 ing the resolving power of objectives. Some physicists have assumed 

 that, owing to the properties of light, when lines approach Avithin a 

 certain distance of each other it is impossible to see them separately ; 

 and that consequently there is a limit to the power of the microscope 

 in this direction, and when that power is attained, further efforts at 

 improvement are useless. This limit has been fixed at different dis- 

 tances by different authorities, and by the same authors at diU'erent 

 times, according as the microscope has been impi-oved, and lines of 

 increasing fineness have been seen. 



Dr. Carpenter, in the first edition (ISoG) of the "Microscope and its 

 Hevelatious," says: "even the J-^- ineh (objective) will probabl}- not 

 enable any band to be distinctly resolved, whose lines are closer than 

 ToVt ^^ ^ Paris line, or y-gg-oQ- of an English inch: ar present, there- 

 fore, the existence of separate lines of a narrower interval than this, 

 is a matter of faith rather than of sight; but there can be no doubt that 



