230 Intelligence and Miscellaneous Articles. 



ration of the annulus, I am inclined to believe that the times you 

 noted are those when the black spots disappeared and appeared. 

 You seem to have been in very nearly the line of the central eclipse, 

 as the least distance of the centres was only 1"*. 



V. A Letter from Mr. Lassell to the Rev. R. Sheepshanks, rela- 

 tive to Observations with a smaU Sextant. 



The sextant, here alluded to, was made by Dollond. It is only 

 3 inches radius, divided to 20', and by vernier reading to 30'' ; but, 

 by means of the reading microscope, subdivisions may be estimated 

 to 10". The telescope magnifies 6 and 11 times; but the higher 

 power is generally used. The whole packs in a box 4'3 inches 

 square, and 2' 7 inches deep. With this instrument Mr. Lassell 

 made a number of observations on various stars, both for the time 

 and latitude, for the express puqoose of determining how near to the 

 truth he might be able to approximate by its means. The observa- 

 tions are given in detail, and the result at which Mr. Lassell arrives 

 is, that under ordinary circumstances the mean of one set of alti- 

 tudes east, and another west, would give the time truly within about 

 one second ; and that a set of each, north and south, at something 

 like equal altitudes, would give the latitude within eight or ten 

 seconds. 



FRIDAY-EVENING MEETINGS AT THE ROYAL INSTITUTION. 



January 18th. — Mr. Faraday on the Gymnotus and Torpedo. 

 The subject included a general view of the nature and condition of 

 electric fishes, with the particular results which the speaker has 

 lately communicated to the Royal Society. 



January 25th. — Mr. Woodward on the apparatus for the public 

 demonstration of the general laws and properties of polarized light. 



February 1st. — Dr. Grant on the recent discoveries regarding 

 the structure and history of animalcules. 



February 8th. — Mr. Parsey on natural perspective. 



February 15th. — Mr. Faraday on Gurney's oxy-oil, or Bude lamp 

 for lighthouses and other situations. 



XXXIX. hitelligence and Miscella?ieoiis Articles. 



ON THE CHLORO-CHROMIC ACID OF DR. THOMSON. 

 To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



IN the number of your Journal for July 1838, (Lond. and Edinb. 

 PhU. Mag. vol. xiii. p. 78.) under the title of Bichromate of Per- 

 chloride of Chromium, there is tin historical error which ought to be 

 corrected. This beautiful substance was not discovered by Berze- 

 lius but in 1824 by Dr. Thomson of Glasgow, and described in the 

 Phil. Trans, for 1827. It has since been examined by Unverdorben, 

 Wohler, Dumas, Rose, and Walter. The following are the formulae 

 which have been deduced from their analyses : — 



» An abstract of Mr. Baily's observations on this eclipse appeared in 

 Lond. and Edinb. Phil. Mag. vol. x. p. 230.— Edit. 



