THE 



LONDON and EDINBURGH 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



♦ 



[THIRD SERIES.] 



SEPTEMBER 1835. 



XIX. On the Double Achromatic Object Glass. By J. W. 

 Lubbock, Esq., V.P. $ Treas. .R.S.* 



TN the Philosophical Transactions for 1821, Sir John F. W. 



A Herschel has entered minutely into the theory of the double 

 achromatic object glass, and has given various useful tables 

 showing the curvatures of the lenses to be employed in order 

 that the spherical and chromatic aberrations may be de- 

 stroyedf. Sir John Herschel seems to have intended to consi- 

 der at some future time the modifications which would result 

 in the inquiry when the thicknesses are not neglected, but I 

 am not aware that he ever carried this intention into effect. 

 I have therefore endeavoured to put the expressions which 

 occur in the theory of spherical aberration in the most ad- 

 vantageous form. In this form they admit of extension to 

 the case when the thicknesses of the lenses and the interval 

 between them are considered, without any difficulty. 



Whether or not opticians will ever trust in great measure 

 to theory for the curvatures of the lenses, taking care pre- 

 viously to ascertain with precision the optical characters of 

 the glass of which they are composed, may admit of doubt; 

 but it would certainly be useful to know the figures of the 

 lenses and other circumstances connected with any large ob- 

 ject glass whose performance is considered perfect, in order 



* Communicated by the Author. 



f A notice of Sir John Herschel's paper will be found in Phil. Mag., 

 vol. lx. p. 147. — Edit. 



Third Series. Vol. 7. No. 39. Sept. 1835. Y 



