WORK OVER DRY MOUNTS, ETC. 301 



objectives of Spencer and Tolles will have but one and 

 the same constant story to tell. With these, properly 

 manipulated, it is impossible to get aught over the po- 

 dura but the exclamation points. With these superb 

 glasses such a thing as the reproduction of the several 

 appearances shown by one and the same scale, as ex- 

 hibited in the cuts by Mr. Michells, becomes an impos- 

 sibility. And here, in the opinion of the author, may 

 be found the key of the problem, to wit: The better 

 glasses showed the podura tolerably well. The poorer 

 ones, those " real honest working glasses,*' of which we 

 have heard so much about, were bound to set forth their 

 individual ^^representations, and thus furnish material 

 for contributions to periodical literature like that of Mr. 

 Michells. 



As to the true structure of podura, there can be 

 little doubt; there has never been but one opinion 

 among American observers accustomed to the use of 

 the finest American objectives, and the spines or ex- 

 clamation marks are accepted as the true resolution of 

 these seales. By the aid of electricity, these spines 

 have been detached from the body of the scale; the 

 detached spine together with the parent scale were 

 photographed and thus presented to the readers of the 

 "Lens." 



We have already had occasion to say that Mr. Geo. 

 W. Morehouse, of Wayland, New York, was the first 

 observer who demonstrated the capabilities of the 

 Beck vertical illuminator; when used in conjunction 

 with American object-glasses of high balsam angles t 



