48 COKEESPONDENCE. 



sees, and tliat it is merely another application of the well-known 

 method of taking rough micrometrie measurements from a scale placed 

 on the stage by the side of the object. But does not this also imjjly 

 the transference or interchange of the retinal impression made on 

 the one eye to that of the other, with an equal visual result ? Or, 

 would not the inference necessarily follow that it must be the purely 

 cerebral perception which we subject to mechanical measurement and 

 delineation ? Can such a solution be accej)ted ? 



The proof, however, that I here offer, the more plausible explana- 

 tion of the observed fact is, I believe, readily afforded by a simple 

 experiment. Hold before the non-observing eye a lucifer-match, or 

 something similar, in the same plane as the prism, an inch or so on 

 one side of it, the spectral image of the match will then be seen inter- 

 posed between the observing eye and the image of the object on the 

 stage refracted into it by the prism. 



To you, sir, as a most competent authority, I submit the matter. 



Yours, &c., 



J. G. Tatem. 



Linear Projection and Eotifers. 



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



Dear Sir, — Permit me to express all due thanks to Mr. Charles 

 Cubitt for his proffered lessons in linear projection, as applied to the 

 delineation of rotifers. And respectfully to decline. That he should 

 select me as his " frightful example," and take so much trouble with 

 the " sole object " of assisting me, is a flattering mark of attention 

 to excite some gratitude, as it certainly does considerable surprise. 

 While giving full credit for excellent intentions, I am constrained 

 to notice some misapj)rehensions and mistakes into which he has 

 unwittingly fallen. He assumes that some, or all, of the figures 

 illustrating my description of (Ecistes intermedins are incorrectly 

 drawn, because he fails to reconcile one with another, in accordance 

 with Ms reading of the laws of linear projection. Well, so much the 

 worse for Mr. Cubitt, for I can assui-e you that the portraits in 

 question are most excellent — thanks to artistic skill not my own — 

 and, without exhibiting affectation of extreme correctness, are yet 

 perfectly amenable to the rules of linear projection when properly 

 aj)plied. It is almost impossible, without a diagram, to show the 

 source of Mr. Cubitt's error and its correction, but a hint or two may 

 suffice. The disk in the ventro-lateral view is inclined at a sharp 

 angle, while those of the other two are foreshortened, and not so much 

 turned dorsally. Thus, any one set of projection lines applicable to the 

 former should, and do, break down with the latter. The side view 

 was not " created " from the back and front views, but drawn under 

 the microscojDe from another and a finer specimen, without reference 

 to compasses or y squares, and yet with a result almost photographic 

 in its truth. 



