1 48 Record of the Royal Society. 



of its record with that of the standard " Campbell-Stokes " instru- 

 ment. 



Theodolites. The number of theodolites tested is also compara- 

 tively small, though it apparently tends to increase. These instru- 

 ments are examined for their optical qualities and accuracy of 

 graduation. 



Sextants. The original testing apparatus was designed by Mr. F. 

 Galton in 1862, and was succeeded in 1866 by a more elaborate 

 apparatus designed by Mr. T. Cooke. In 1888 the Admiralty made 

 a regulation that all sextants used by cadets of H.M. Navy must be 

 certificated at Kew. Sextant shades are separately examined by 

 means of a special apparatus already alluded to. 



Compasses. Prior to 1890 only a small number of compasses were 

 verified, and these consisted mainly of small azimuth compasses for 

 use by travellers. Of late years a very considerable number of ships' 

 compasses have been examined. During the present year the test 

 for ships' compasses has been revised and extended, with the assist- 

 ance of Captain Creak, F.B.S., of the Hydrographic Department, so* 

 as to bring it more into line with the Admiralty test, and with the 

 scientific requirements of the day. 



Telescopes and Binoculars. The testing of navy telescopes and 

 binoculars, on behalf of the Admiralty, was undertaken in 1889, andi 

 a good deal of similar work has since then been also performed for 

 instrument makers and private persons. 



Lenses. Since 1891 photographic lenses have been tested, with 

 the aid of the apparatus devised by Major L. Darwin, to which 

 reference has already been made. This departure has, however, met 

 with somewhat limited public recognition, little over 100 lenses 

 having been as yet sent for examination. These are included under 

 the heading " Miscellaneous " in the subsequent table. 



Watches and Chronometers. The rating of watches was commenced 

 in 1884, the system of verification following pretty closely that pre- 

 viously adopted at Geneva. Three classes of certificates, A, B, C> 

 are issued A denoting the highest grade according to the severity 

 of the test for which the watch is entered; and an annual list is- 

 published of those watches which obtain 80 per cent, and upwards o 

 full marks in the competition for a class A certificate. The number 

 of watches tested annually has fluctuated considerably, a maximum 

 of 1,521 having been reached in 1893. Of late years the tendency 

 has been to a reduction in the numbers entered for the lower classes,. 

 B and C, of certificates, and an increase in the number entered for 

 class A. 



The rating of marine chronometers commenced in 1886. Two 

 classes of certificates, A and B, of which A is the higher, are granted 

 to instruments sent for the ordinary trials. In answer to special 



