1 EEPORT 1869. 



Assistant, was sent to Armagh to examine the Barograph there, and to Sand- 

 wick-mause, Orkney, to superintend the erection of an anemometer. The 

 expenses have, on both these occasions, been repaid by the Meteorological 

 ■Committee. 



In conclusion, the Kew Committee desire to bring under the notice of the 

 British Association, that the system of automatic records established and in 

 actual ■n'ork at the Kew Observatory, comprehends magnetic, barometric, and 

 thermometric observations, as well as those of the direction and velocity of 

 the wind, to which an electric self-recording instmment will soon be added. 

 They think that it would be very advantageous to magnetical and meteo- 

 rological science if a fully illustrated work were published descriptive of these 

 instruments, and of the method of working them, together with the method 

 of reductions actually employed. 



J. P. GASSIOT, CUirman. 

 Kew Observatory, 

 15th July, 1869. 



APPENDIX. 



A Description of the Means adopted by the Meteorological Com- 

 mittee for ensixriug Accuracy in the Numerical Values 

 obtained from their Self-recording Instruments. 



(Extracted, with permission, from the Eeport of the Meteorological Committee.) 



In the first Eeport of this Committee the principles of construction of their 

 self-recording instraments were fully described, and enough was said to ren- 

 der it probable that good results would be obtained ; but the final method 

 of tabulating from the traces of these instruments was not then decided on, 

 nor had any scheme been devised for ensuring accuracy in the tabulated 

 numerical values. 



The labours of the Committee in this department have been materially 

 aided by suggestions from the superintending Committee of the Central (Kew) 

 Observatory, and also from the Directors of the various outlying observatories, 

 and as a result the Committee are now satisfied that the process of examina- 

 tion to which the tabulated values are subjected before reaching the central 

 office is such as to afford a satisfactory guarantee of accuracy. 



It may be a fitting sequel to the description of these instruments (already 

 given), to give here an account of the method adopted for ensuring accuracy 

 in the results which they afford. 



In the first place, the nature of the various instrumental errors and the 

 best method of avoiding these may with propriety be described, and in the 

 next place it may be desirable to give in detaU the code of regulations 

 adopted by the Committee for the guidance of their various observatories. 



BAEOGRAPn. 



The values of atmospheric pressure derived from this instrument are 

 liable to have their accuracy affected by tliree causes : — 



(1) By an imperfect temperature compensation. 



(2) By a sluggish action of the mercury in the Barograph tube. 



(3) By imperfection in the system of recording and tabulating. 



Temperatuye compensation. — The method by which the Barographs are 

 compensated for temperature has been described in the Report of the 

 Meteorological Committee for the year 1867. The precise position of the 

 fulcrum of the glass rod was determined by means of some preliminary expe- 



