146 . Record of the Royal Society. 



black bulb maximum thermometers in vacuo. On the grass near the 

 stand are minimum thermometers of various kinds. These several 

 thermometers are read daily at 10 A.M. 



Eye observations of the amount of sky covered by clouds, with the 

 nature of the clouds and apparent directions of motion, are taken 

 daily at 10 A.M., noon, 2 P.M., 4 P.M., and 10 P.M. The scale used is 

 for a perfectly clear sky, 10 for a completely clouded one. 



Surrounding the garden is grass land, fnlly 5 acres in extent, 

 which was added to the Observatory holding leased from the Crown 

 in 1894. It is enclosed within a 6-foot park paling. 



Verification Work. 



This work took its origin at tbe middle of the present century in 

 the want then felt in England for magnetic and meteorological instru- 

 ments of greater accuracy and trustworthiness than those previously 

 in use. It rapidly expanded, and in the natural process of growth 

 has come to include the examination of instruments and appliances 

 whose connexion with magnetism and meteorology is remote. 



Magnetic Instruments. One of the most important branches of the 

 verification work is the determination of the constants of magnetic 

 instruments. A considerable proportion of the magnetometers and 

 inclinometers hitherto used in magnetic surveys have been examined 

 at the Observatory. Since the construction of the magnetographs, in 

 1856, twenty-one Observatories have been supplied with similar 

 instruments, and the majority of these had been previously tried at 

 Kew. 



Thermometers. In 1850 a standard thermometer, verified, it 

 appears, by Regnault, was obtained from Paris, along with a dividing 

 engine and other necessary apparatus for calibrating and examining 

 thermometers. Within a few years from that date, in addition to 

 verification work, a large number of standard thermometers had been 

 made. The construction of these thermometers still forms a part of 

 the Observatory work, although not to such a large extent as was 

 formerly the case. Since 1850 over 700 standard thermometers have 

 been made up, of which fully 600 have been issued to other Observa- 

 tories, physical investigators, and instrument makers. 



At first the thermometers verified were intended almost exclusively 

 for meteorological work. Towards the middle of the decade 1860- 

 1870, however, clinical thermometers began to be verified, and in the 

 course of a few years the number of thermometers increased beyond 

 the capabilities of the simple testing apparatus originally in use. 



To meet the exigencies of the case an apparatus was designed by 

 Mr. F. Galton, which allowed of the nearly simultaneous comparison 

 of a large number of thermometers at any specified temperature 



