streugtlieniug equatorial ridge of solid metal, tilled with com- 

 mercial kerosene. A short section of copjier tubing with the 

 walls flattened on two sides for convenience of manipulation 

 during construction is soldered to a suitable opening in one 

 pole of the coiJ2:)er globe, and the free end of the heavy tube is 

 likewise soldered to a small copper tube with an external diam- 

 eter of about 4 millimeters and an internal diameter of 1 milli- 

 meter. This tube is also tilled with j^etroleum and may be of 

 any reasonable length up to 10 meters or i:)erhaps more without 

 vitiating the accuracy of the instrument to any apjireciable 

 extent. Furthermore, in practise this tube may be variously 

 bent and curved in making adjustments without detriment to 

 the results obtained (fig. 1, C). 



Fig. 1. — Hallock thei'mograph. A, bulb containing kerosene. B, 

 heavy tube, soldered to polar opening in bulb. C, capillary tube con- 

 necting bulb with expanding chambei-. D, double expansion chamber. 

 E, upright post with adjustment clamp at E, on expansion chamber 

 and fastened to short lever arm at F. G, lever extending from axis, 

 and bearing pen, which traces temperature record on the cylinder. H, 

 adjustment to raise or lower pen in making corrections and calibrations. 

 K, cylinder driven by internal clockwork which makes one revolution 

 per week. The cylinder carries paper ruled horizontally to degrees 

 centigrade. The rate of movement carries the paper past the pen at 

 such rate that two hours is taken to pass over the interval between two 

 curved lines. L, upright rod on hinged base to remove pen from con- 

 tact with paper. M, base of cast iron. 



The free end of the capillary tube is connected through an 

 opening in the side wdth the chamber in the interior of a solid 

 brass block fastened to the base of the apparatus. Two pairs 

 of convex, corrugated brass disks 8 centimeters in diameter 

 are fastened together at the edges and the united pairs are then 

 soldered together forming an expansion chamber comj^osed of 

 two disk-shaj^ed cells, with an opening through the soldered 

 portion (tig. 1, D). Next an opening is made in the center of 

 one of the convex surfaces and this opening is joined by solder 

 to the chamber in the brass block. The double expansion 

 chamber is also tilled with petroleum and care is taken to ex- 

 clude all air from the tubes and chambers. The entire system 

 is now seen to consist of a I'igi^l bulb, tubes, and small base 



