TABLE OF CONTENTS 



TO THIS FIRST VOLUME. 



APRIL 1797. 





I. J. HE Principles and Application of a New Method of conftruding Achra- 

 matic Telefcopes. By Robert Blair, M. D. — — page 1 



Imperfeftions of achromatic lenfes — arife chiefly from the glafs. Propofed remedy by theufe of 

 fluids. Prifmatic apparatus for meafuring the refradlive and difperfive qualities of fluids. Hadley'i 

 quadrant applied to meafure the abfolute refraftive denfities. Enumeration of the optical proper- 

 ties of various fluids. Conftruftion of a lens including a fluid. Obfervations. New and linguUr 

 cafes of refrangibilicy — Explanation. Coloured fpeftra formed by different mediums are not divi- 

 ded into proportional intervals — Confequence of this, and its remedies. The doftrine of optical- 

 iiberration from figure, and method of otvialing it ; from Huyghens — .'Application to telefcopes. 

 Imperfeftion of compound lenfes from the want of perfeft compenfation in the contrary power* 

 of difperfion through the whole fpeftrum. Difcovery of an adequate remedy. Conftruftion of 

 lenfes, in which the aberrations from figure and difperfion of colour are both removed. Prefent 

 ftate of the invention. 



II. A remarkable Effeft of the Inflexion of Light pafllng through Wire Cloth, 

 not yel clearly explained — — — — P- ' 3 



Singular appearance of a diftant lamp feen through an handkerchief. Variation of the experiment — 

 Inferences — Remarks on thofe inferences, and new experiments. Dcdudlions. Exp.-rimcnts with 

 wire cloth. Extremely brilliant folar fpeftrum. Obfervations. 



HI. Defcription of an Inftrumenc wliich renders the Eledricity of the Atmo- 

 fphere and other weak Charges very rceptible, without the Poflibility of an 

 equivocal Refiilt — — — — p. 1 6 



Hiftory of the inTCDtion. Defcription of a fpinning inftrumcnt— Iti power. 



IV. Obfervations on the Art of printing Books and Piece Goods by the Action 

 of Cylinders — — — — — p. 1!^ 



Thret methsdi of writing— by the pen or brufh — by the type or block— and by the engraved plate. 



a 2 Lfi r! 



