294 CHAY ROOT FOR DYING RED. 



je6l, may not fall perpendicularly upon them. Bending the 

 frames will noteffed this purpofe, for the glaffes muft be pa- 

 rallel, as reprefented in Fig. 2. where A B reprefents the 

 frame^ cc and dd, the two glafles. 



I have a pair of fpedtacles conftrud^ed in this maimer, but 

 fo contrived, that the glafles may be fet to any angle, to (how 

 the different ejffecls of oblique and perpendicular rays. 



The theory of Dr. Wollafton*s patent fpeftacles, may be 



thus examined. 



and that the roe- Let the lens LL be taken away from Fig. 1. and a me<- 



nifcus is not fu- nifcus of the fame diameter and focal diftance be drawn in 



double convex. ^^^ place. Then the rays rs, rt, after pailing through this 



lens will meet at (p) as before, becaufe this lens is of the fame 



focal diftance as the double convex, by Hyp. 



Confequently thefe rays will fall upon the eye aty, in the 

 fame flate of convergency as before. Whence a lens of the 

 menifcus form, poflefles no properties, in theory, fuperior to 

 the double convex. 



E. WALKER. 



XIL 



Communication refpeSling the Chay Root, a Species of Madder 

 ufed for dying durable red Colours in the Eafi Indies, By 

 John Stockwell, £fq. * 



Introduaory XYiR. STOCKWELL prefents his compliments to Mr. 



Ta Yor^ ^'^' Taylor, with a fample of an article called CJiaya Root, for the 

 infpedion of the Society for the Encouragement of Arts, ^c. 

 It is in much ufe on the Coromandel coafl, for dying. He ac- 

 companies it with a ftiort extrad, which will afford fome 

 information concerning it. 



If Mr. T'4ylor fliould caufe any experip[ients to be made upon 

 it, Mr. Stockwell will be obliged by being favoured with the 

 refult; and if any perfon diould think favourably of it, and be 

 defirous of a quantity, no doubt it may be had. 



Eaji-India IVarehoufes, 

 Crutched Friars, 23d May, 1803. 



* Made to the Society of Arts, Adeli^hi, and printed in Volume 

 XXL of their Tranfa6lions, 



2 Extraa 



