34-0 



Abstract of a Meteorological Journal kept at Benares during the Years 

 1824, 1825, and 1826. By James Prinsep, Esq. Assay Master of 

 the Mint at Benares. Communicated by Peter Mark Roget, M.D. 

 Secretary of the Royal Society. Read January 25, 1828. [Phil. 

 Trans. 1828,jo. 251.] 



The registers, of which the monthly results are presented in a 

 tabular form, contain an account of the states of the barometer, 

 thermometer, the air hygrometer, the wet bulb hygrometer, the de- 

 grees of aqueous tension, amount of evaporation, quantity of rain, 

 wind, and other circumstances relating to the weather at Benares 

 during three successive years. The author states it as his opinion, 

 that the diurnal oscillations of the barometer, as well as the monthly 

 variations, are dependent on the alterations of the specific gravity of 

 the air from changes in its temperature ; the operations of which may 

 be traced with much greater distinctness at Benares than in the more 

 variable climates of Europe. He illustrates his position by graphic 

 representations of the changes in the barometer, corresponding with 

 those of the thermometer. 



He next points out a method of reducing the indications derived 

 from hygrometers of different constructions, to absolute degrees of 

 aqueous tension : and concludes, by expressing a hope that the cul- 

 tivators of hygrometrical science in Europe would take pains to fur- 

 nish standard instruments of comparison at the several principal 

 stations on the Indian continent; as such a measure is the only secu- 

 rity which can be obtained against inaccuracy in the observations that 

 are now very extensively carried on in that part of the world. 



A Description of a vertical floating Collimator ; and an Account of its 

 application to Astronomical Observations with a Circle and with a 

 zenithTelescope. By Captain Henry Kater, V.P.R.S. Read April 24, 

 and May 1, 1828. [Phil. Trans. 1828,^9. 257.] 



The construction of the instrument which forms the subject of this 

 paper, is a material improvement on that of the horizontal floating 

 collimator, of which an account was given by the author in the Phi- 

 losophical Transactions for 1825. Its superiority is derived from its 

 adaptation to the vertical instead of the horizontal position, by which 

 the sources of error arising from the necessity of transferring the in- 

 strument to different sides of the observatory, and of taking the float 

 out of the mercury and replacing it, at each observation, are wholly ob- 

 viated. The vertical floating collimator has the further advantage of 

 being adapted for use, not only with a circle, but also with a tele- 

 scope, either of the refracting or reflecting kind. Such a telescope, 

 furnished with a wire micrometer, and directed to the zenith, becomes 

 a zenith telescope, free from all the objections to which the zenith 

 sector, and the zenith telescope, with a plumb line, are liable. 



The instrument itself is supported on a square mahogany stand, 

 which slides on two parallel beams fixed at the upper part of the ob- 



