225 



The instruments with which the observations accompanying this 

 paper were made, are a five-, and a seven-feet equatorial ; the former 

 was constructed under the direction of the late Capt. Huddart, and 

 is remarkable for its extreme lightness, for the promptitude with 

 which it obeys its adjustments, and for its ability in retaining them. 

 Its object-glass, of 3f- inches aperture, and of five-feet focal length, 

 is the work of the late P. and J. Dollond ; whilst its divided circles, 

 microscopes, &c., were completed by Messrs. J. and E. Troughton. 

 A description of it is given, and a drawing is annexed. The latter 

 is a telescope of 7 -feet focal length, and five inches clear aperture ; 

 it was made by Tulley, and is mounted on the polar axis of the old 

 equatorial sector, made by Sisson for the Royal Observatory, and 

 for the use of which, acknowledgment is made to the Council of this 

 Society. 



The micrometers employed are the work of Mr. Troughton, and 

 have long since been familiar to astronomers under the name of 

 Troughton's Wire Micrometer. The measures of distance are all 

 central. Various precautions employed in conducting the observa- 

 tions are narrated ; contrivances whereby some difficulties were sur- 

 mounted are enumerated. The observations of each star were ge- 

 nerally made in each other's presence, but occasionally in different 

 parts of the observatory, and with different instruments, without any 

 communication with each other. In some instances the observations 

 of Mr. Troughton or Mr. Richardson have been appealed to, in order 

 to settle discrepancies. 



To the observations of each star the authors attach their mean 

 result ; the results obtained by other observers are also placed in the 

 order in which they were made ; b<!it there is one circumstance to 

 which they solicit attention, namely, that as far as Sir William Hers- 

 chel's observations are concerned, the dates and results will not ac- 

 cord with those published by Sir William in the Transactions, for 

 reasons which will be found in a former part of the paper. 



As an appendix, measures of a few stars less perfectly observed are 

 added, which, although not entitled to equal confidence with the 

 others, the authors think may perhaps still have their use. 



On the Effects of Temperature on the Intensity of Magnetic Forces ; 

 and on the Diurnal Variation of the Terrestrial Magnetic Intensity. 

 By Samuel Hunter Christie, Esq. M.A. of Trinity College, Cam- 

 bridge, Fellow of the Cambridge Philosophical Society : of the Royal 

 Military Academy. Communicated by the President. Read June 

 17, 1824. [Phil. Trans. 1825, ;>. 1.] 



The details of the author's experiments upon the above subjects 

 are given in an extended series of tables, commencing with a tempe- 

 rature of 3 Fahr. up to 127 Fahr. Mr. Christie found that as 

 the temperature of the magnets increased, their intensity diminished, 

 in direct contradiction to the notion of destroying magnetism by in- 

 tense cold. From a temperature of 80 the intensity decreased va- 



VOL. II. Q 



