354 REPORT — 1851. 



lithographic impressions printed, by first procuring in the copper-plate press 

 an impression from the gelatine tracing itself, on the lithographer's " Transfer 

 Paper," and by then printing from that impression transferred to the stone 

 (as usual)*. 



TheApfaratus of Polishing-hoards, Coating and Mercurializing Boxes, &c., 

 remains nearly as described at p. 184, Report for 1850. 



Four small poHshing boards of this kind have been made, and seem to be 

 improvements upon the frames employed by Daguerreotypists usually. 



Mr. Dent's Chronometer, a Sextant, and an Artificial Horizon, 

 have been used for keeping Greenwich mean time. The two latter instru- 

 ments were sent by Colonel Sabine from Woolwich. 



The Apparatus not (or very little) used 



in this year, and belonging to the Association, or on loan to it, is enumerated 

 in our MS. catalogue with all the above. 



Books 



presented to the Association by foreign Societies and by individual Donors in 

 this year have been added to our little library, which now comprises about 

 150 volumes, exclusive of pamphlets and of the MS. Catalogue of Stars, &c. ; 

 the remaining number of complete sets of the Reports of the Association 

 (to July 31, 1850 inclusive) at Kew is 24. 



Some of the Royal Society's Instruments 

 sent here very recently for careful preservation will be forthwith catalogued. 



II. OBSERVATIONS. 



The observations at Kew in this year have chiefly related to investigations 

 on the interesting subject of Frequency of atmospheric electricity, and a pro- 

 minent object of the inquiry has been the attainment of data for the addition 

 of proper apparatus to a Photo-electrograph of the kind formerly describedf, 

 whereby the study of this subject may be facilitated by means which appear 

 to me peculiarly well calculated for the purpose. 



The form of our Electro-meteorological Journal remains as described in 

 my Report for 1844, with the exceptions observable in the annexed specimen 

 and the following revised account. 



In column A is stated the time of each observation by the Dent's chrono- 

 meter, which " was kept always very near to Greenwich mean time by occa- 

 sional sextant observations of tlie sun and by casual comparisons, by means 

 of a pocket watch, with standard clocks in London. The epochs noticed in 

 this column are, — 1st, the time of the barometer observation, which was about 

 the middle time of the ordinary meteorological observations. The tempera- 

 ture of the air and the hygrometer were observed before the barometer, and 

 the wind, weather, &c. immediately thereafter; 2nd. the time of observing 

 the elec ti ical tension of the air and of the commencement of the frequency 

 observation ; and .'frd, the time when the electrometer was considered to have 

 re-acquired its full tension after discharge." 



* The tabulations and gelatine tracings produced during " the course of experimental 

 trials," will, at its termination, belong, I presume, to the Royal Society (bv agreement), 

 t Vide Phil. Trans. Pt. I. for 1847. 



