INDUSTRIAL PROGRESS DURING THE YEAR 1875. xxxvii 



necessary to correct for the projection of the stem of the 

 thermometer beyond the bath in which the bulb is immersed. 

 The author, having made nearly two thousand observations 

 for each of the instruments used by him, concludes that the 

 w T ell-known expression given by Regnault does not agree 

 with his experiments; he shows the exact nature of the 

 errors of his own instruments, but concludes that every ob- 

 server must make a similar investigation of his own ther- 

 mometers. 



Among: the numerous new methods of mechanical resristra- 

 tion of atmospheric phenomena, especial attention seems to 

 have been secured for the meteorographs of Baumhauer, 

 Rysselbergh, and Secchi. 



An excellent self-recording mercurial barometer is de- 

 scribed by Redier; and a mega-barometer, or one that meas- 

 ures the pressure of the air at any moment on an enlarged 

 scale, has been constructed by Hirn. 



Among self-recording thermometers, the most peculiar is 

 that of Mr. Cripps, which is so constructed that the move- 

 ments of the mercury in the tube of the thermometer disturb 

 the position of equilibrium of the whole instrument, inasmuch 

 as it is delicately poised on two pivots. The consequent 

 movement, which is due essentially to the force of gravity, 

 is made serviceable for the purpose of registration. 



Constitution of the Atmosphere. Williams has made a pho- 

 tometric investigation into the intensity of twilight when the 

 sun is at various distances below the horizon. He finds that 

 at one minute after the sun sets the intensity of the radiation 

 is T ^j- ; at ten minutes after sunset it is fW Both this and 

 the following investigation give us a means of expressing rel- 

 atively the amount of moisture in the air. 



Crosby, of the Massachusetts Institute of Technology, has 

 made some photometric determinations of the light of the 

 sky at different distances from the sun. The results, repre- 

 sented graphically, show a logarithmic curve when the in- 

 tensities are plotted as ordinates, and the natural sines of 

 the sun's angular distance as abcissag. 



The application of the spectroscope to the determination 

 of the quantity of moisture in the atmosphere has been si- 

 multaneously studied independently by De Sains, in France, 

 and Tait and Smythe, of Edinburgh. The latter agree that 



