268 Angular AjpeHures of Objed-glasses. Bij Jcibez Hogg. 



readers of the Journal with a more detailed exposition of his 

 reasons for considering the slit " a valuable adjunct," while the 

 method in which he would employ it is so entirely at variance with 

 Mr. Wenham's. I am perfectly aware that when Mr. Wenham 

 first brought forward his slit method he wrote, " it is preferable to 

 open the slit till the edges appear in the margin of the field ;" * 

 but in a later paper vindicating his report on the aperture of 

 Tolles' ^th, he appears to have abandoned this specific direction as 

 to the size of the slit, and he now relies on some infinitesimally 

 naiTow slit, which he says should " cut off all lateral pencils " ; 

 however, with Professor Eobinson's modified method no slit is 

 required, and most conclusive and reliable results will be obtained. 



* ' M. M. J.,' vol. xi., 1874, p. 118. 



