848 



which is found in but two or three places in a country, because there 

 is no fear, even if this should ever be rendered a common plant, that 

 a sufficient number of others will not remain rare, especially since it 

 is likely that as the study of Botany extends, there will be a greater 

 demand for rare plants. On the contrary, I think we have every 

 reason to thank a botanist for his kindness in propagating a rare 

 plant, not so much for the pleasure we ourselves are to derive from 

 it, as for the pleasure it will in all probability afford to the bota- 

 nists who are to succeed us. — G. G.Mill; Kensington, December 

 9, 1843. 



Erratum. — Phytol. 813, line 9 from bottom, for " Lateral " read 

 " Latent." 



AlRT. CXCIIT. — Proceedings of Societies. 



MICROSCOPICAL SOCIETY OF LONDON. 



Novemher 15, 1843. — J. S. Bowerbank, Esq., F.R.S. &c. in the cLair. 

 Mr. A. White read a paper describing the application of a lever movement to the 

 stage of a microscope. It consists of a lever, to the shorter arm of which a ball is 

 firmly screwed, moving in a socket formed by the upper plate of the stage, and a cup, 

 which is a brass plate secured by two screws to that plate. This lever passes through 

 a perforated ball, moving in a socket formed by an arm attached to an immoveable 

 part of the microscope, and a cup formed and secured upon the arm, as in the former 

 instance. This lever is about five inches long, having the longer arm equal to three 

 and the shorter to one. This proportion however varies according to position, and 

 hence the necessity of a perforation in the second ball to allow for it. This construc- 

 tion affords great facility of motion in every direction, and the range in the instrument 

 exhibited was three quarters of an inch. 



Mr. Jackson read a paper describing an improvement in the mode of applying a 

 divided glass micrometer to the measurement of objects under examination, described 

 by him in a former paper read September 3, 1841. The micrometer is mounted in a 

 thin brass frame, which slides easily (under a spring) through slits in the opposite 

 sides of the eye-piece, which slits, when not in use, are closed by a quarter revolution 

 of an internal tube having similar slits. Its divisions are ^ of an inch apart, with one 

 of the spaces divided into five by finer lines, which, as they may be readily brought by 

 the sliding of the micrometer into contact with the magnified edge of the object to be 

 examined, aff'ovd great facility of measurement. Mr. Jackson concluded with some 

 observations relative to the mode of using this instrument, and of finding the value of 

 its divisions under the various circumstances in which it may be employed. — /. W. 



