PHOTOMETER

(Yunanca köken — orijinale bakınız.) lights were An instrument for measuring the intensity of light, or of illumination. of Sirius The most elegant instrument which goes under this name which '« the photometer is invented merely the by the differential late Sir John thermometer Leslie. of It only the (1.) the same ingenious philosopher, having small portion one of its balls diaphanous, and the other with Sirius; coated with China ink, or blown of deep he 27064 black enamel; and the whole covered Cosmotheoros.) by a case of thin transparent gla , to deproposed fend the balls from the disturbing influence called of currents of air. The photometer has extremely two general forms; the one portable (fig. greatest ^> 1.) in which the black ball is about an on paper inch higher than the other, and bent forward to the same vertical line, or the axis of the translucent cylindrical case; reserved and the other stationary (fig. 2,) having both its balls of the relative same height, and reclining in opposite ways; the case being winter composed of a wide cylinder surmounted by the larger seg series of ment ofa hollow gla sphere. The latter form of the in- Iished strument, though le commodious, is better adapted for nice Traiti observations; since, besides receiving the light more reguappeared larly,its balls, from bcw» on3 'heN same level, are not liable rear a one a red [s. 943]