[ H'T ] 

 XXV. hitelligeiice and Mucellaneuus Articles. 



ON THE ABKRRATIONS OF COMPOUND LENSES AND OBJECT- 

 GLASSES. 



A VERY valuable paper on this subject, by J. F. \V. Herschel, 

 Esq. F.R.S. &c. which was read before the Royal Society m 

 March 1821, appeared in Part II. of the Philosophical Trans- 

 actions for last year, the important object of which is to render 

 the abstruse researches of celebrated geometers wlio have oc- 

 cupied themselves with the theory of the refracting telescope, 

 Ijracticallv available for the construction of good instruments: 

 and to present, " under a general and uniform analysis, the 

 whole theory of the aberrations of spherical surfaces, by fur- 

 nishhig practical results of easy computation to the artist, dis- 

 entangled from all algebraicarcom})lexity, and applicable, by 

 interpdations of the simi>lest possible kintl, to all the ordmary 

 varieties of the materials on which he has to work." 



The length of the paper, and the ))ressure of more recent 

 matter, will not permit us now to insert it. It may, however, 

 be useful to jiresent our readers with the practical result m 

 the words of Mr. Herschel himself. 



" We may announce it as a practical tlieorem, which in all 

 probabilitv 'will be found sufficiently exact for use, that a 

 double obiect-glass will be free from aberration, provided the 

 Kidius of the exterior surface of the crown lens be 6-720, and 

 of the flint ] 4-20, the focal length of the combination being 

 10-000, and the radii of the interior surmces being computed 

 from these data, by the fonnuke given in all elementary works 

 on optics, so as to' make the focal lengths oi the two glasses m 

 the direct ratio of their dispersive jK)wers." \\ e are hai)py to 

 learn that the intelligent author, whose words we have quoted, 

 is about to extend his inquiries on this subject, 

 t 



VOYAGE OF SURVEY AND DISCOVERY. 



I'owards the close of last year an expedition was fitted out 

 from Dcptford, consisting of the Leven and Baiaceuta, from 

 which accomits have \ntcn lately received, announcing that on 

 the 28lh of May tl.ev were about to proceed on the UirtUer 

 objects of their vovao'c. The Persian Gulf and the .led Sea 

 were to be particularlv explored and surveyed. At uo Janeiro 

 a binall vessel was purchased to add to the s(iuadron. lUe 

 whole is under the command <.f C'apt.W. F.^^ .Owen, a gen- 

 tleman every way (i>iali(ied for such a voyage, a^.slsted by pro- 

 per officers, with' a number of v<.img gentlemen destmed tor 

 hitnre objects of the same nature. No necessary expense was 

 .snaretl in lilting out this expedition with all the reqitis-.tc m- 

 ' ° ']' 2 slrumcnls 



