I 



British Association. I2i 



A dipping circle constructed by Gambey will be placed on a 

 pijiar at the remote end of the room ; and will be furnished with a^ 

 needle, whose axis is formed into a knife-edge, for the purpose of 

 observing the diurnal variations of the dip. Gauss's large appara- 

 tus will also be set up in the same room, and will be used occasion- 

 ally, especially in observations o^ the absolute intensity y made ac- 

 cording to the method proposed by that distinguished philosopher.* 



The bars are too large to be employed in conjunction with other 

 magnetical apparatus. 



It is intended to combine a regular series of meteorological obser- 

 vations, with those on the direction and intensity of the terrestrial 

 magnetic force just spoken of; and every care and precaution has 

 been adopted in the construction of the instruments. 



In conclusion, Mr. Lloyd said, that he felt it a duty to allude to 

 the liberality and zeal in the cause of science which had been evin- 

 ced by the Board of Trinity College on this occasion. The proba- 

 ble expense of the building and instruments is estimated at 1000/. ; 

 and that sum was immediately allocated to the purpose, when it ap- 

 peared that the interests of science were likely to be benefited by 

 the outlay. 



Mr. Peacock congratulated the Section upon the prospect held 

 out to the scientific world, of having fixed magnetical observatories 

 erected in such places as would afford the surest promise of success- 

 ful co-operation, particularly when they would be placed under the 

 superintendence of gentlemen so eminently qualified for the task as 

 Professor Lloyd. He informed the Section, that an observatory 

 for magnetical observations had been erected at Greenwich, and 

 that little doubt need be entertained of the rapid advances which 

 the interesting investigations connected with this important science 

 would now receive. — Mr. Ettrick conceived, that bricks would be 

 a very improper material for the construction of a magnetical ob- 

 servatory. He considered the use of metals in any part of the building 

 as highly objectionable ; even copper as fastenings or hinges to doors 

 would not be free from injurious effect. He made some inquiries 

 as to the mode of reading off, proposed by Professor Lloyd. — Prof. 

 Stevelly said, that Mr. Ettrick was unquestionably right in the ob- 

 jection urged against the use of bricks, but Professor Lloyd had dis- 

 tinctly stated, that bricks were not to be used, and that experiments 

 had been made to ascertain the precise magnetical influence, if any 

 there was, of the kind of stone which it was proposed to use. It 

 was well however, that Mr. Ettrick's observations should go abroad, 

 for the guidance of persons not conversant with these subjects* 

 Bricks, when built into large edifices, such as the chimneys of fac- 

 tories, were well known to have acquired magnetic polarity : the ma- 

 terial from which they were made must be largely impregnated with 

 iron : the mud of rivers was the detritus from hills, whose rocks 

 were often highly magnetic. The engineers employed on the trigo- 

 nometrical survey of Ireland had erected a mound of stones com- 



• Prof. Gauss's description of hi? apparatus and mode of observing 

 vill he fomul in Lond. & Edinb. Phil. Mag., vol. ii. p. 29L 



Phil. Mag. S. 3. Vol. 12. No. 71. Suppl. Jan. 1838. R 



