164 RESEARCH 



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 anyone 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, thermo- 

 meters 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. 



c The observatory also possesses a dividing-engine 

 by Perreaux, by means of which standard thermo- 

 meters are graduated. It was purchased by a grant 

 from the Royal Society. 



' In this room the pure water required for photo- 

 graphic processes is obtained by distillation ; and 

 here also a small transit telescope is placed for ascer- 

 taining 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 the higher storey is the workshop, containing, 

 among other things, a slide-lathe by Whitworth, and 

 a planing machine by Armstead, both of which were 



