G. H. Williams — Petrographical Microscope. 115 



benefits from the application of the microscope as her sister 

 sciences, biology and medicine ; and there seems to be no good 

 reason why this instrument should not be made of as much 

 educational value in her field as in theirs. 



Not all who study the natural sciences are able or care to 

 become original investigators. The scientific training, how- 

 ever, possesses for every one certain peculiar advantages, and 

 the organic sciences have not been slow to appreciate how val- 

 uable a factor in such a training the microscope may be made. 

 Five years of practical experience have convinced the writer 

 that the microscope in geology may, with as great success, be 

 employed for purely educational purposes. 



If then the microscope be of such use in geology, both as a 

 means of research and as an educational discipline, the pro- 

 duction of instruments especially designed for rock- study be- 

 comes a matter of importance. Such a demand has for some 

 time past been met, with varying success, by several Continental 

 manufacturers ; but, owing to the limited interest in micro - 

 geology on this side of the Atlantic, the attempts of American 

 makers to supply petrographical microscopes have hitherto 

 been wholly inadequate. 



. The advantages to the constantly increasing number of pet- 

 rographical students in America, of a suitable instrument of 

 home manufacture, are too apparent to need enumeration. In- 

 deed, the actual demand for such an instrument has been so 

 often and so urgently forced upon the writer's attention, that, 

 at his request, the well-known Bausch and Lomb Optical Com- 

 pany of Rochester, N. T., undertook the construction of a 

 purely petrographical stand which should satisfy all the de- 

 mands for mineral and rock study and at the same time come 

 within the means of geological students. Each essential point 

 was designated by the writer and has been elaborated by the 

 manufacturer in the simplest and most inexpensive manner con- 

 sistent with satisfactory results. The instrument in its present 

 shape, though it may be subject to further improvements, offers 

 at a reasonable price ($135.00) a complete petrographical and 

 mineralogical microscope of excellent workmanship, possessing 

 all essential features, and several advantages (such as a sliding 

 analyzer and mechanical stage) to be secured only on the more 

 expensive European stands. 



It has been thought that a figure and description of this 

 microscope would prove of interest to all whose attention is 

 devoted to geology, whether as teachers or as investigators. . 



The accompanying cut shows the instrument constructed 

 upon what is known as the Bausch and Lomb " Model Stand." 

 (See Bausch and Lomb Illustrated Catalogue for 1887, pp. 15.) 

 This has a frame of japanned iron, with brass tube, stage and 



