xlii REPORT — 1859. 



Meeting of the Association on the Self-recording Magnetical apparatus at 

 the Observatory ; but the Report is in progress of completion by Mr. Stewart, 

 and will be printed in the next volume of the Transactions of the Association. 



An instrument has been devised at the Observatory for tabulating the 

 values of the magnetic elements from the curves given by the Magnetographs. 

 As the staff of Assistants at the Observatory is not sufficiently large to under- 

 take these tabulations, General Sabine has undertaken to have the results 

 tabulated at Woolwich lor every hour ; but the instrument is capable of 

 furnishing data for much smaller intervals, and may under special circum- 

 stances be thus used. 



The observations connected with the Magnetic Survey made in Scotland 

 by Mr. Welsh, are in progress of reduction by Mr. Stewart, and the result 

 will be presented as a report to the present meeting. 



Self-recording Magnetic Instruments designed for the first of the Colonial 

 Observatories which have been proposed to Her Majesty's Government have 

 been completed by Mr. Adie, from drawings prepared by Mr. Beckley from 

 the design of the late Mr. Welsh, and are set up in a wooden house erected 

 near the Observatory, for the purpose of affording an opportunity to the 

 proposed Magnetical observers to be instructed in the use of the Self-record- 

 ing Instruments. 



Since the last meeting of the Association the unfortunate death of Mr. 

 Welsh has retarded the experiments with the Photoheliograph, but from time 

 to time they have been gone on with, at first by Mr. Chambers, who obtained 

 some very fair results, and latterly by Mr. Beckley, as his other duties have 

 permitted ; and in order that they might be prosecuted more continuously, 

 the Committee have fitted up a Photographic room in close contiguity to the 

 instrument. This addition to the photographic establishment has been at- 

 tended with the most promising results ; and the Committee have satisfaction 

 in reporting that the difficulties which have hitherto presented themselves in 

 the way of a daily photographic record of the sun, appear to be almost 

 entirely surmounted. Since the erection of the photographic room, Mr. 

 Beckley has been enabled to make a series of experiments, and has turned 

 his attention to the exact determination of the chemical focus of the Photo- 

 heliograph, which there was reason to suspect did not correspond precisely 

 with the visual focus ; for although the chromatic aberrations of the object- 

 glass had been specially corrected in order to obtain that result, the second- 

 ary glass, which magnified the image, was not so corrected. It has been 

 found, after repeated trials, that the best photographic definition is obtained 

 when the sensitized plate is situated from y^th to -1-th of an inch beyond the 

 visual focus in the case of a 4-inch picture ; and that when this adjustment 

 is made, beautiful pictures are obtained of the sun 4 inches in diameter, 

 which still bear magnifying with a lens cf low power, and show considerable 

 detail on the sun's surfaces besides the spots, which are well defined. 



Mr. De la Rue, by combining two pictures obtained by the Photohelio- 

 graph at an interval of three days, has produced a stereoscopic image of our 

 luminary which presents to the mind the idea of sphericity. 



Under Mr. De la Rue's direction, Mr. Beckley is making special experi- 

 ments having for their object the determination of the kind of sensitive sur- 

 face best suited for obtaining perfect pictures ; for it ha3 been found that 

 the plates are more liable to stains of the various kinds, known to photo-- 

 graphers, under the circumstance of exposure to intense sun-light, than they 

 would be if employed in taking ordinary pictures in the camera. 



Now that the photographic apparatus has been brought to a workable 

 state, Mr. De la Rue and Mr. Carrington, joint Secretaries of the Astrono- 



