_ PERSPECTIVE INSTRUMENT. Ill 



tance of the object glafs, and D the focal diftance of theeye- 

 glafs. Then-— - = the magnifying power. 



But C : D : : A : B. (Smith's Optics, p. 93.) And by df- 



O \ 



vifion -—=-—. Therefore the enlargement of the picture 



D B 



of an object within the telefcope, does not increafe its mag- 

 nifying power. 



Hence thefe properties of the telefcope prove to a demon- Conclufion. 

 juration, that the conclufion which I have drawn from my 

 experiments is a law of vifion ; and this law (hows us, that no 

 concavity of the Iky; no terreftrial perfpective, nor even the 

 painting of the waves under Black- Friar's Bridge, can explain 

 the phenomenon in queftion *. The caufe lies wholly within 

 the eye. 



' It is a mod unpleafant talk to enter into controverfy, but I Refpeding con, 

 cannot fee how I could avoid it in this inftance. It appears to 

 me, Sir, that you inferted C. L.'s paper for me to anfv^er, 

 and I have complied; hoping, however, that this is the laft 

 time of my having occafion to u(e my pen, againft an anony- 

 mous writer. Common juftice feems to demand the names of 

 thole who undertake the examination of fuch papers as are 

 owned by their refpective authors. 



I am, Dear Sir, 



Your moft obedient fervanf, 



EZ. WALKER. 

 Lynn, Jan. IS, 1805. 



XII. 



Defcriplion of a fimple Infirument for making correct Drawings 

 from Nature. By T. C. B. 



To Mr. NICHOLSON. 

 SIR, January 22, 1805. 



JL HE defcription of two inftruments for facilitating land- 

 fcape drawing from nature given in the firft volume, page 

 281, of your Journal, has fuggefted to me the conftruclion of 



* Phijofophical Journal, vol. IX. page 237. 



another, 



