Instruments and Historical Relics. 173 



3. Open Cistern Mercurial Barometer, by Ramsden. 



1 Phil. Trans.,' 1776, p. 383. 



4. Open Cistern Mercurial Barometer, by Newman, under the direc- 



tion of Mr. Daniell. ' Meteorological Essays.' 



5. Open Cistern Mercurial Barometer, by Newman, under the direc- 



tion of Sir H. Davy, with an Iron Plunging Cylinder, compen- 

 sating for difference of capacities. 



6. Mercurial Standard Thermometer, by Dollond. Brass divided 



scale, 23^ inches long, with divisions extending from 20 below, 

 to 535 above zero, Fahrenheit. 



7. Mercurial Standard Thermometer, by Troughton and Simms. 



Brass divided scale, 15 inches long; divisions from zero to 

 215 F. 



8. Wedgwood's Pyrometer; or Thermometer for measuring high 



degrees of heat. 66 parts. 



' Phil. Trans.,' 1782, p. 305 ; 1784, p. 358 ; 1786, p. 390. 



9. Captain Kater's Hygrometer, by Robinson. 



10. Jones's Hygrometer, with the stem bent at an acute angle. 



' Phil. Trans.,' 1826, p. 53. 



11. Hydrometer, by Fordyce. 



12. Huygens's Aerial Telescope. 



(1) An object-glass of 122 feet focal length, with 

 an eye-glass of 6 inches, and original appara- 

 tus for adjustment, made by Huygens, and 

 presented by him to the Royal Society in 1691. 



(2) The apparatus for using Huygens's object-glass, >12 parts, 

 constructed by Hooke. 



(3) Additional apparatus, by Dr. Pound. Presented 

 by Dr. Bradley. 



(4) Ditto, by Mr. Cavendish. 



13. An Object-glass by Huygens, of 170 feet focal length. Presented 



to the Royal Society by Sir Isaac Neivton, P.R.S. 



14. An Object-glass by Huygens, with two eye-glasses by Scarlet, for 



a Telescope of 210 feet. Presented by the Rev. Gilbert Burnet, 

 M.A., F.R.S., in 1724. 



15. An Object-glass (Venetian), of 90 feet focal length: which 

 belonged to Flamsteed. Presented to the Royal Society by James 

 Hodgson, F.R.S., in 1737. 



16. A 10-inch Protractpr, by Ramsden ; with vernier to 1'. 



17. Convertible Pendulum of Captain Kater; with the Agate Planes. 



The basis of the present system of British Weights and Measures. 



' Phil. Trans.,' 1818, p. 37. 



18. Copy of the Imperial Standard Yard, by Dollond. 



' Phil. Trans.,' 1831, p. 345. 



