Radiometer and Sunshine Recorder. 161 



had in adjusting, and position of c. g. of the balance changed 

 by changing its weight. On the beam next the blackened 

 tube is a track on which runs the carriage E. This carriage is 

 attached by the wire method, or by two universal motions to 

 the arm F, which, in turn; is fastened to the nut Gr. The arm 

 motion is limited to a right line parallel to the track by a rod 

 which runs through a hole in the arm. 



The nut Gr, which also carries the pen, is moved backwards 

 and forwards by the screw H, geared to the perpendicular 

 shaft I, which is -broken by the universal motion J. The 

 lower end of the shaft passes through a square block of soft 

 iron, which block is limited by guides to a to-and-fro motion 

 between the magnets K, Kl ; it then terminates in a gear 

 wheel which engages either one of the wheels L, LI, according 

 to which magnet is excited. A. clock-work motor M, run by a 

 weight and governed by a fly-wheel, turns the shaft, on which 

 are the two gear wheels L, LI, always in the same direction. 

 This motor is started or stopped by the magnet N, the arma- 

 ture of which moves a check to the fly-wheel. 



From the back of the beam, in the middle, is a long pointer, 

 terminating in platinum contacts (shown at the end of the 

 beam in the drawing to avoid confusion). One or the other 

 of these contacts, on the slightest motion of the beam, touches 

 the point R or Rl. The contact R is connected with the mag- 

 net K, and the battery and the contact Rl with the magnet 

 Kl and the battery. The other pole of the battery runs 

 through the magnet X and to the plate B on which the knife 

 edge of the beam rests ; the plate and the arm F being insu- 

 lated, only the scale beam is in circuit. 



The' tubes are filled with pure mercury and set in place in 

 the same manner and with the same precautions as in filling a 

 barometer tube, a liberal amount of mercury being left in the 

 cups; the connecting tube is filled and put in place; then 

 enough absolute alcohol is injected into each tube to insure, 

 under all conditions of temperature and pressure, a saturated 

 vapor of alcohol at the top. 



An addition is built to the south side of an ordinary weather 

 bureau shelter for thermometers, having a flat top and the 

 same louver board sides; over a large hole in the top is put a 

 glass cover ; one-third of its circumference on the north is cut 

 out and louver boards put in ; on north side of the middle of 

 the top of cover (not in middle as shown in cut) some form of 

 lantern top is put. The ventilation must be as free as possible. 



When the sun is not shining both tubes are of the same 

 temperature and the tension of the alcohol vapor is the same 

 in each ; both tubes weigh the same, and the machine is in 



