CORBESPONDENCE. 83 



A Substitute for the Tint-glass Reflector. 



To the Editor of the ^Monthly Microscojncal Journal.'' 



Upper Holloway, December 18, 1873, 

 Sir, — I wish to call the attention of those interested in microsco- 

 pical work to a modification of the existing apparatus used for micro- 

 scopical drawing. The instrument I use and which I find more 

 serviceable than any other for this purpose, on account of its simpli- 

 city, consists of the thinnest possible covering glass placed at a proper 

 angle in front of the eye-piece of the microscope. The advantage of 

 this thin film of glass over the camera lucida, the neutral tint reflector, 

 or the steel disk, is that it enables the pencil to be easily followed in 

 tracing the image which is thrown upon the paper below. An ordi- 

 nary piece of white glass does not answer the purpose, as it throws 

 two pictures of the object. This doubling of the image is reduced to 

 nothing in proportion to the thinness of the glass. The instrument 

 which I have had made for me by Mr. Sutton, instrument maker, 108, 

 Holloway Eoad, is sold at a very moderate price. It is composed of a 

 brass collar to affix to the eye-piece of the microscope ; this carries two 

 light brass arms, between which, mounted in a brass ring, revolves 

 the glass, so that it may be placed at the required angle. 



I remain, Sir, yours, &c., 

 W. Kesteven, Jun. 



An Error in Mr. Plumer's last Letter. 



To the Editor of the 'Monthly Microscopical Journal.'' 



January 12, 1874. 



Sir, — "Will you allow me to correct a misprint in my letter in the 

 January number of your Journal? At the beginning of the line 

 towards the end of the first paragraph, instead of lith read ^th. 



Believe me, yours faithfully and obliged, 



J. J. Plumer. 



Prototaxites. 



To the Editor of the 'Monthly Microscopical Journal.'' 



McGiLL College, Montreal, Jan. 1, 1874. 



Sir, — Though I do not propose to continue the controversy which 

 Mr. Carruthers has raised respecting Prototaxites, I must ask permission 

 to direct the attention of your readers to three points in his rejoinder 

 in your November number. 



First, he abandons a great part of the essential conditions of the 

 case in the statement that " the mode of occurrence of the fossil has 

 nothing whatever to do with the matter." This statement neither I 

 nor any other palaeontologist can admit. In the study of any doubtful 

 fossil, geological age and conditions of occurrence, fossil associates 

 and state of preservation furnish most valuable guidance ; and neglect 

 of these aids has been a fruitful source of error. 



Secondly, in the one point to which he now narrows his argument, 



