ON THE KEW OBSBRVATOftY. 339 



proposed magnetic vibration experiments ; it is high enough to allow an ob- 

 server to stand in it, and broad enough to allow him to view the electro- 

 meters in a stooping attitude. Several parts of the contained apparatus are 

 similar to the principal corresponding parts in our Dome (vide Report for 

 1844, p. 120). Some are improved. 



a is a mahogany varnished cylinder fitted into a circular aperture in the 

 roof, and furnished with a smooth ring or rim projecting outward from the 

 upper end. 



B, a window (which may serve for photographic purposes, &c.). 



C, my strong hexapod-stand ; but capable of being folded into a very small 

 compass*. 



c', a safety conductor of thick copper wire, in good conducting commu- 

 nication, with moist earth or water. 



D, fig. 3% is the upper end of the principal conductor, which is a light 

 conical tube of copper 12 feet long. 



E, a brass tube whose upper end is 2^ feet above the roof of A, and into 

 which the lower end of D is firmly screwed, but from which it can be re- 

 moved at pleasure by a person standing on the roof of A. 



F, the usual stout hollow glass pillar, with its collar of wood, &c. It is 

 trumpet-shaped below and firmly secured by bolts passing through the collar 

 and table. 



G, the table, which also carries the other instruments. 



H, the cap with a globular ring fitted on F, and supporting 



II, which are two conical tubular arms of brass. 



KK, the bolts, &c. which contain the screws, plugs, and stoppers for sus- 

 taining and adjusting the sliding arms, &c. 



k' P, the clamping balls. 



k-, one of the sliding arms passing through K, &c. and adjustable ver- 

 tically (or to any angle). It can be secured in any required position by 

 means of A', in the manner formerly described. 



L, the small warming lamp. 



l^, the usual conical chimney of copper, closed above and entering F, to 

 which it imparts warmth from L. 



M, fig. 3% a small Volta's lantern, fitted by a socket on the top of D. It 

 contains the collecting lamp, and is provided with a little cowlf in lieu of 

 the former perforated cap. 



N, a copper cylindrical parapluie, fitted by a collar on E, and having a 

 smooth ring or rim, projecting nearly as much inward as the rim of a' pro- 

 jects outward |. 



O, the uninsulated part of Volta's standard or electrometer No. 1. 



P, his second electrometer, both r,s improved and formerly described. 



QQ, the usual apparatus, of suspending wire, glass tubes, covers (of O 

 and P), rings, &c., by means of which the straw pendulums are made to 

 depend for insulation on F only. 



R, the horizontal tubular arm, fixed upon k% with its stoppers and notches 

 (for the reception of the knife-edges in the rings). The eye-pieces and 

 their adjusting apparatus used in the Dome for reading the scales of the 



* First described in 1828. r?rf« "Mechanical Perspective," p. 19. 



t This cowl was (long since) suggested by the Astronomer Royal and is a decided im- 

 provement. 



t These improvements on the old parapluie, &c. (which did not exclude every drop of 

 water during a violent driving shower) occurred to me since the reading of this Report, and 

 are adopted in a complete electrical apparatus now constructing for the Royal Madiid 

 Observatory. 



z 2 



