346 REPORT — 1851. 



from Col. Sabine. The length of its arbitrary scale (beautifully etched 

 upon the tube) is 17 inches. The range is from —5 to +235, and the 

 number of divisions is 650. 



The boiling-point (as determined on April S, 1851) is at the 591st divi- 

 sion, and the freezing-point at the lOOdth. 



A Standard Thermometer by Ronchetti, has been also received from Col. 

 Sabine. 



The freezing-point (as determined on April S, 1851) is at the 31°*4 

 division. 



A Machine for dividing right lines in equal parts, on Ramsden's principle, 

 but very ingeniously modified by M. Perreaux, with appendages for fixing 

 calibring and graduating thermometer-tubes, has been, very seasonably, 

 imported and added to our collection under the auspices of Mr. Gassiot. The 

 important application of M. Perreaux's machine to the above-mentioned and 

 other purposes was effected with the aid and advice of M. Regnault ; and 

 the instrument, together with the modes of using it, have been clearly de- 

 scribed and illustrated by M. Soulnier in a Report of July 8, 1846, in- 

 serted in the ' Bulletin des Sciences*.' 



Apparatus for testing the graduation of Thermometers, and some for com- 

 paring them and for determining the freezing- and boiling-points, formed 

 other portions of Mr. Gassiot's valuable importation. 



Barometers. 



The Mountain Barometer by Newman {vide Report for 1844), formerly 

 suspended freely, and not quite vertically, at the N.E. window of the 

 Quadrant Room, is now fixed at the central window of that room by means 

 of an adjustable screw above and an adjustable bracket below for ensuring 

 perpendicularity. 



" The frame-work of the barometer is of wood, a brass scale 13 inches 

 long being affixed. The diameter of the tube is 0-1? inch. There is no 

 adjustment for the different capacity of the tube and cistern. The neutral 

 point is 29-764 inches. The capacity -^ and the capillary action +0*043. 

 The brass scale does not extend to the cistern. The height of the cistern 

 above mean water is 



A Standard Barometer by Newman has been sent by Col. Sabine from 

 Woolwich, and is fixed near to the eastern wall of the Transit Room. It is 

 mounted in a metallic frame, and is the same in principle as that made for 

 the Royal Society. It is furnished with the improved iron cistern (for faci- 

 litating transport). It has not been compared with the Royal Society standard. 

 " The diameter of the tube (bore) is 0'55 inch. The height of its cistern 

 above mean water is ." A thermometer whose bulb is plunged in a short 

 tube containing mercury has been fixed near to the column on the back- 

 board, for temperature corrections of the column. 



ThePhoto-Barometrograph,^\ace(\ near the central window of the Quadrant 

 Room, is the result of several improvements upon experimental apparatus 

 used here in August 1845f. It has been alluded to in former Reports, &c., 



* A trivial addition of clamps has been made here for applying it to the graduation of 

 magnetograph scales, &c. 



t And described in the Phil. Trans., Part I. for 1847. 



