86 



Report of the Kew Committee, 



Ten Standard Thermometers have also been calibrated and divided, 

 and supplied to societies and individuals during the year. 



The following miscellaneous instruments have also been verified : — 



Hydrometers 47 



Anemometers 3 



Rain Gauges 6 



Theodolites , 3 



Sextants 25 



Index Glasses for ditto, unmounted 23 



Horizon ,, ,, ,, 26 



Coloured Shades ,, „ 188 



There are at present in the Observatory undergoing verification, 

 8 Barometers, 395 Thermometers, and 7 Hydrometers. 



A considerable increase having taken place in the number of 

 Sextants submitted for verification, the Committee, after due con- 

 sideration, have withdrawn the old form of certificate of examination, 

 and substituted a more general statement of the efficiency of the in- 

 strument, recognising in future two classes of sextant; Class A in 

 which the total error of the instrument, from any cause, nowhere 

 exceeds thirty seconds ; and Class B where the limit is a maximum 

 error of three minutes of arc. 



The schedule of fees payable for the verification of instruments 

 has been revised, and copies of the new scale, together with par- 

 ticulars as to the transmission, &c, of instruments to and from the 

 Observatory for the purpose of comparison, have been widely dis- 

 tributed amongst opticians and instrument makers. 



Standard Barometers. — From time to time comparisons have been 

 made between the two Welsh Standard Barometers, the old Royal 

 Society Standard, and Newman No. 34, the working Standard of the 

 Observatory. The Portable Standards of the Observatory have also 

 been employed in making comparisons of the Standard Barometers at 

 the Hydrographic Office, Admiralty, the University Museum, Oxford, 

 and the Royal Engineering College, Cooper's Hill. 



A metal plate, engraved with an inscription stating the history of 

 the old Royal Society Standard Barometer, and giving details of the 

 method employed in filling it on the occasion of its recent repair, has 

 now been affixed to the instrument. 



The large difference formerly observed in the heights of the mer- 

 curial column in the flint and crown glass tubes of this barometer, has 

 not been found to exist in the refilled tubes, and the mean difference 

 between their indications is now less than 0*001 inch. 



Standard Thermometers. — The Committee has exchanged Standard 

 Thermometers with the Johns Hopkins University, U.S.A., Professor 

 Rowland having on the occasion of his recent visit to this country 



