496 Report of the Kew Committee. 



the collimators through damp, it was thought advisable to fit new and 

 improved scales to all of them. On being furnished with the 

 necessary drawings, Captain Abney kindly had the set of photographs 

 made in his laboratory, and they were duly fitted to the collimators 

 by Mr. Adie. 



Care was taken to replace them exactly in the same positions 

 as those occupied by the old scales, and after they were set up a re- 

 determination of all the angles was very accurately made and recorded 

 for future use. 



Steps have recently been taken with a view of fitting electric lamps, 

 worked by a storage battery, to the instrument for testing the 

 parallelism of the dark shades, in order that this operation may be 

 performed in the absence of brilliant sunshine, a condition which 

 has hitherto rendered it impossible to complete the examination of 

 these shades in cloudy weather. 



Sextant Telescopes. The Committee, having had their attention 

 drawn to the low optical power of some of the telescopes supplied 

 with sextants submitted to them for examination, have given instruc- 

 tions that no certificate of the highest class should be issued with any 

 instrument if the telescope is not capable of distinguishing the 

 smallest angle exhibited by the division of the graduations on the arc 

 of the sextant. 



The Hydraulic Press used for testing the behaviour of deep sea 

 thermometers under hydrostatic pressures of 3^ tons per square inch 

 is riot capable of exerting the higher pressures now required by the 

 Admiralty for thermometers employed in the deeper soundings. 



The question of strengthening the press was submitted to Messrs. 

 Armstrong a:id Co., who reported that the cost of doing so would 

 exceed the sum the Committee could afford to expend upon the 

 apparatus, 



Normal Thermometers. The Committee having considered the 

 desirability of having some thermometers accurately compared with 

 the hydrogen thermometer of the Conservatoire des Poids et Mesures, 

 at Paris, instructed Mr. Whipple to convey to the director of that 

 office the set of three closely graduated mercurial thermometers, 

 whose calibration errors were investigated in 1879, by Professors 

 T. E. Thorpe and Riicker (see 'British Association Report,' 1881, 

 p. 540), and also an alcohol thermometer graduated at Kew for the 

 special purpose of the comparison, its scale extending from 100 to 

 + 90 Faht. The examination of these thermometers has now been 

 completed, and M. Benoit has sent his report upon them to Kew 

 Observatory. 



In addition to the usual instruments submitted for verification, the 

 Committee have been called upon for special examination and reports 

 referring to the following articles : the Admiralty, for a Gun Director 



