The Diacafoptron. 127 



phrases which have not been used, and to seize upon ihem 

 as a subject of ridicule. This is the case with some pro- 

 posed elegant change, and with jny supposed reconuneii- 

 datioa to transfer chennstry to the " (ire-side of the draw- 

 ing-room :" expressions which I have not used, and yet 

 upon which Dr. Pearson has thou^lu proper to be exlreinely 

 jocular. 



I have only further to add, that sliould Dr. Pearson again 

 write upon the subject, I shall not easily he induced to re- 

 sume the controversy. I am sorry^ therefore, to see it inti- 

 niated at the conclusion of his paper that he proposes to 

 continue his observations in your next Number ; and as it 

 appears that those intended remarks are n)eant as a return 

 for the notice which f have taken of his papers, f regret the 

 more that he should take so mucli trouble. For'praise, 

 when used as the vehicle of irony, is the worst kind of cen- 

 sure. The discovery of truth ouglu to be the only object 

 of philosophical discussion. There are, doubtless, many 

 errors in my hmnble attempts at chemical analvsis ; but 

 unless Dr. Pearson points out those errors, or bi-mgs for- 

 ward new facts connected with my inquiries, I confess that 

 f had nmch rather he would not again honour them with 

 his notice. 



" Quicquid id est, timeo Dauaos et dona ferentes." 



I remain, sir, &c. See. 



Russel Square, Feb. 21, 1812. AlEX. MarcET. 



V 



XX. Description of the Dincaloptron. Comnuaiicutt'd iij 

 JJr. GiBEEs, of' Bath. 



T 



ARrous optical instruments have l)epn applied to the 

 purposes of drawing and copying, and have been carried to 

 a great degree ot perfection. The Camera obscura, the 

 Delineator, and Camera lucida, have severally been justly 

 celci. rated for the facility ot tracing outlines, and the rules 

 of perspective have been correctly illustrated by these re- 

 presentations f)f n;itt!rHi objects on a plam surface. 



The great simplicity of ihe instrument now about to be 

 described, may entitle it to rank amonii the most u'-elul of 

 the kind, as, to the ad-'antage of its siiii|)lc siructure and 

 applicability without straining the eyes, it adds a degree of 

 truth not to be exceeded. Without' the aid of adcHiional 

 reflecting surfaces, this instrument represents its objtcl'> :is 

 an ordinary mirror, at the same time that it allows sutti- 

 cienl transmitted light to pass for the guidance of the hand 

 behind it. Thus, by a very lillle management, both the 



liand 



