ON THE KEW OBSERVATORY. 335 



declination have been in a great degree remedied. All the essential parts of 

 the apparatus being of metal or stone, the permanency of the adjustments is 

 secured. The light being admitted directly to the instrument, and the op- 

 tical power not being so great, the photographic means are increased. The 

 dimensions of the magnet and its appendages being much smaller, the me- 

 chanical inertia is diminished ; and by the use of a very powerful copper 

 damper, the inconvenience arising from vibration is almost wholly got rid 

 of. The results of these improvements are such as might be expected. It 

 has been found that a long series of registrations can be obtained without 

 the occurrence of a single case of mechanical derangement requiring re-ad- 

 justment of any portion of the apparatus. The instrument has been found 

 capable of recording, in a perfectly distinct manner, almost all the magnetic 

 changes which occur, and with a delicacy of scale quite sufficient to repre- 

 sent even the most minute movement. In only one instance during the six 

 months has it been unable to overtake the most rapid motions. In the dis- 

 turbance of September 29, it certainly has been found deficient in power to 

 represent with distinctness those very violent and extensive changes which 

 occasionally do occur. This deficiency seems to have arisen — 1st, from the 

 length of time during which the plate is exposed to the action of the light 

 being sufficient for more than one motion to take place; and 2nd, from 

 the mechanical inertia being still so great, as in some instances to carry the 

 magnet farther in the direction of a sudden magnetic change than is strictly 

 due to such change. These defects seem to point to the desirability of 

 further improvements in the same direction as those already made, namely, 

 greater photographic power and less mechanical inertia. It should be re- 

 marked also, that in the larger disturbances the extent of scale adopted for 

 all the instruments has been insufficient to contain the extreme excursions. 



The performance of the vertical force instrument has unfortunately been 

 so little satisfactory, from causes apparently unconnected with the means ne- 

 cessary to adapt it to photographic registration, that it is impossible to come 

 to a distinct conclusion as to its value. Its performance for some time after 

 being repaired by the maker was, however, so good, and its power of exhi- 

 biting such great and sudden motions as occurred during the disturbance of 

 September 3-4 so considerable, as to hold out the expectation that, when- 

 ever the source of the errors already noticed shall have been discovered, it 

 may be found to be a really efficient and trustworthy instrument. 



John Welsh. 

 . Kew Observatory, October 23, 1851. 



leport concerning the Observatory of the British Association at Kew, 

 from August 1, 1850 to July 1, 1851. By Francis Ronalds, £'*§-., 

 F.R.S., Honorary Superintendent. 



iIt is hoped that this eighth annual summary relative to the status and pro- 

 [ceedings of the Kew Observatory will evince our sincere desire to promote 

 'the liberal views of the British Association, and that our diligence has been 

 commensurate with the augmented funds which have been kindly granted by 

 Her Majesty's Government and the Royal Society, and with the increased 

 interest which gentlemen of the highest scientific acquirements and repu- 

 tation, both at home and abroad, have manifested in the success of the Esta- 

 blishment. 



