Rojjal Asirmbmicat 1^oMet§) ^ 



matter, so far as this is an American discovery, it is only under 

 the auspices of the Department of the Coast Survey of the United 

 States, and with the facilities and means furnished by its present 

 enlightened superintendent, Dr. A. D. Bache, that the application of 

 electro-magnetism to the purposes of geodesy and of astronomy has 

 been successfully accomplished. =9noo-. -^sbxfdfa o.Lt oJ ir>v/oq ^jvijoat 



Extract of a Letter from Mr. Lassell. 5] 



" I have been very busy, and have brought to a most successfv^q 

 issue my efforts to support my two-foot speculum free from sensiblat 

 flexure. All has gone on well and come right at once; and the^ 

 speculum having been once placed in the tube, I have neither,i 

 reason nor inclination to take it out again. I was pretty sanguine^, j 

 yet must acknowledge the result has gone beyond my hopes. I aa-itr 

 nounced the details of the plan to the British Association at Edin^ 

 burgh*, and there is a clear and sufficient description of it in the 

 Report just about publishing, or perhaps already out. I have scarcely 

 varied at all in carrying it out. I have found 27 or 28 levers suf- 

 ficient : and these are about as many as can be conveniently applied 

 without interfering with the 1 8 discs and levers for zenithal support. 

 Moreover, I have found cementing fulcral blocks of speculum metal 

 upon the back with plaster of Paris quite efficient — firm enough to 

 bear twice the requisite strain. Each lever, in a horizontal position 

 of the tube, supports 15 lbs. of the speculum's weight; diminishing, 

 of course, as the telescope approaches the zenith, where they are 

 inactive. The superiority of action of the telescope since the ap- 

 plication of this apparatus, I think none but myself who have seen 

 it in both states can yet appreciate, and the atmosphere now alone 

 remains my formidable and unconquerable foe, as it is indeed of 

 all large apertures. So tenderly is the metal sustained in all posi- 

 tions, that no part of it can ever come into contact, with more than 

 the pressure of a few pounds, against the tube or box in which it 

 is placed. The plan seems to me applicable to specula of two or 

 three times the diameter of mine with equal success. I was scarcely 

 prepared to believe beforehand that the bending would follow so 

 regular a law, as that it should be completely eliminated by a re- 

 gularly devised system of counteracting support. I believe the ap^, 

 plication of the apparatus does not add more than 40 lbs. toJJ^^^.j 

 end of the tube which contains the speculum. ^aoaniiq 



"Did I mention to you that I had (some time ago now) mad© 

 an addition and improvement to the polishing machine by com- 

 municating a regular slow motion to the polisher ? It has given me^ 

 some trouble and looks complex, but it is efficient, and tends, X,, 

 think, to greater uniformity of curve.v pj^whea I. have leisure, J^t> 

 must describe it more fully." // <''Vtf/^'>;4^ »— ^ 



Occultation of a Fixed Star by Jupiter. By the Rev. W. I^^'f 

 Dawes. ■'^t:? 



1851, May 8, 9^ G.M.T. Having turned my 8|-foot refract<?r" 



* Reports of the Twentieth Meeting of the British Association, 1850] 

 Notices and Abstracts, p. 180, &c. On a method of supporting a large ^ 

 speculum, free from sensible flexure, by Mr. Lassell, &c. "^ ' 



