4 - SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 50 



a soldered tin case. This, in turn, is surrounded by a larger wooden 

 box, having ten spiral chair-seat springs fastened within, so as to 

 give elastic support to the inner case. To prevent too much move- 

 ment of the inner case, wads of excelsior are put between the boxes 

 at the eight corners. To prevent severe jarring of the outside box, 

 wads of excelsior in canvas are also tacked outside the outer box 

 at its eight corners. 



Besides the three pyrheliometers mentioned, two have been sold 

 by the Institution to the United States Weather Bureau and to the 

 Physical Laboratory of the Agricultural Department of the United 

 States. Three others are being prepared by request for use in 

 South America — one at Arequipa, Peru, two in Argentina. 



With each instrument is sent out a calibration sheet, and also the 

 following : 



Directions for Using the Abbot Silver Disk Pyrheliometer 



Setting Up 



The pyrheliometer is in the long box; the mounting in the cubical 

 box. 



1. If the mercury column of the thermometer is broken, remove 

 the little screw at the side near the upper end of the nickel-plated 

 tube, and take off the upper portion of the tube. Then heat the 

 exposed stem cavity of the thermometer gently in a smoky flame 

 (a match flame is good) until the mercury is expelled from the 

 cavity. Then, holding the thermometer vertical, shake the instru- 

 ment repeatedly with a downward jerk until the mercury columns 

 join. 



2. Remove the two little ivory plugs (using pliers if necessary) 

 and unscrew the two brass screws under them, and also unscrew the 

 third similar screw seen through the trunnion on the other side of 

 the case. About three complete turns of each screw is proper. 

 Insert the two ivory plugs. When packing the instrument again 

 for a journey, screzv in the three screws as far as they \vill go. 

 Their purpose is to clamp the silver disk to protect the thermometer 

 during transportation. 



3. Unscrew the two pivots from the sides of the ring of the 

 mounting, insert the pyrheliometer so that the thermometer is not 

 next to the worm wheel, and screw in the pivots. 



4. Unclamp the half ring and set the polar axis approximately 

 for the latitude of the place. The thermometer should be next to 

 the upper end of the axis. 



