xlii REPORT — 1860. 



ratus (described by Mr. Welsh in the ' Transactions' of the Royal Society, 

 vol. 146. p. 507) for verifying and comparing marine barometers with the 

 standard. This room has also accommodation for the marine barometers 

 sent for verification. In the middle of the room is a solid block of masonry, 

 extending through the floor to the ground below. To this an astronomical 

 quadrant was formerly attached ; it is now used as a support for the standard 

 barometers. This room contains also a Photographic Barograph invented 

 by Mr. Francis Ronalds, which, though not at present in operation, may 

 serve as a model for any one who wishes to have an instrument of this 

 description. It is described by Mr. Ronalds in the Report of the British 

 Association for 1851. 



In a room to the west of the Library, thermometers for the Board of Trade, 

 the Admiralty, and opticians, are compared with a standard thermometer by 

 means of a very simple apparatus devised by the late Mr. Welsh. 



The Observatory also possesses a dividing-engine by Perreaux, by means of 

 which standard thermometers are graduated. It was purchased by a grant 

 from the Royal Society. 



In this room the pure water required for photographic processes is obtained 

 by distillation; and here also a small transit telescope is placed for ascertain- 

 ing time. The transit instrument is erected in a line between two meridian 

 marks — one to the north and the other to the south of the Observatory ; so 

 that, by means of suitable openings, either of these marks may be viewed by 

 the telescope. 



In a higher story is the workshop, containing, among other things, a slide- 

 lathe by Whitworth, and a planing machine by Armstead, both of which were 

 presented to the Kew Observatory by tiie Royal Society. 



In the dome is placed the Photoheliograph for obtaining pictures of the 

 sun's disk ; attached to the dome there is a small chamber in which the 

 photographic processes connected with the photoheliograph are conducted. 

 This chambe ns supplied with water by means of a force-pump. A self- 

 recording Robinson s anemometer j.«also attached to the dome. 



In addition to the rooms now specified, there are the private apartments 

 attached to the Observatory. 



On the north side of the Observatory there is an apparatus similar to that 

 used at the Toronto Observatory for containing the wet- and dry-bulb, the 

 maximum and the minimum thermometers. 



The model magnetic house, elsewhere alluded to in this Report, stands at a 

 distance of about 60 yards from the Observatory ; and the small wooden 

 house in which the absolute magnetic observations are made, at a distance 

 of about 110 yards. These houses are within a wooden paling, which fences 

 them off from the remainder of the Park, and encloses about one acre of 

 ground attached to the Observatory. 



The work done may now be briefly specified. In the first place, the self- 

 recording magnetographs, as already mentioned, are kept in constant opera- 

 tion, and record the changes continually occurring in the magnetic elements. 



The photographs are sent to General Sabine's establishment at Woolwich, 

 to undergo the processes of measurement and tabulation. 



In the model magnetic house there is at present a set of magnetographs 

 which Dr. Bergsma will take to Java. When this set is removed another will 

 supply its place, in readiness for any other Observatory, colonial or foreign, 

 at which it may be required. 



In the house for absolute determinations, monthly values of the declination, 

 dip, and horizontal magnetic force are taken, and magnetic instruments for 

 foreign or colonial observatories have their constants determined. 



