390 Scientific Notices — Miscellaneous. [Nov. 



These pearls are of a very fine ivater, and nearly orbicular ; 

 their base is supported by a small process which separates at 

 the end into two short divero^ing processes, which stand off at 

 right anjrt^les to the central rib ; on more minute examination it 

 appeared that these pearls were produced by there being in-* 

 troduced between the mantle of the animal (while yet alive) 

 and the shell, a small piece of silver wire, bent into a peculiar 

 form, that is to say, so as to form a right angle, with one arm 

 ending in two diverging processes, so as to make the simple 

 end always keep its erect position. These wires must be intro- 

 duced in the same manner as the seitii-orbicular pieces of 

 mother of pearl in the other method of forming artificial pearls, 

 as there is no appearance of any external injury. The pearls 

 are solid and nearly orbicular, with a small pedicell, which is 

 continued so as to entirely cover the wire. They may be per- 

 forated and used so as to show their whole surface, which I did 

 not expect could ever be the case with any artificial pearls ; but 

 they must doubtless, unlike the artificial pearls formed by the 

 other means, be a considerable time in coming to any useful 

 and valuable size. 



MlSCEXXANEOUS. 



13. Greenwich Observations, 



The follov/iug extract of a l^tt^r, addressed by Professor 

 Bess?l to Professor SphumacJber, appeared in the last No. of 

 the journal of Science.--" Whe^i I had the pleasure of bein^ 

 your gu^st^t Altona, you showed me the numbers of the Philo- 

 sophical Magazine, which contain a very severe censure of the 

 Gveenwi9li Observations for 1821. I saw this censure with 

 some surprise, bepause I had always considered the collection 

 of obs^rv^tipris at Greenwich as singularly valuable, and as a 

 mh source :0f ast;-onoraic^l truths ; nor wer'e you, 1, believe, of a 

 differeut opipipti, and we vvere perfectly agreed respecting the 

 ur^iinportAiji^pe qf the inaccuracies that were imputed to this work 

 in tii^tY^P,, papers published in the 64th volume of tiie Philo- 

 sophical Muoazine. For those who are acquainted with the 

 Greenwich pbservations, and who compare them with the critic's 

 remark?^ eve^y further explanation would be superfluous, but 

 since it may be supposed that these remarks will fall into the 

 hands of many persons not well versed in astronomy, I readily 

 comply with the request which you made, that I would commit 

 to writing our common view of the subject. I feel, as well as 

 yourself, the propriety of doing my best on the occasion, in 

 order that too great importance may not be attached to this 

 censure of an establishment, to which astronomy is indebted for 

 a great proportion of its advancement *, and that its importance 

 cannot be very great, is sufficiently shown by the facility with 



