ACTION OF THE TROPICAL SUN. 



119 



The galvanometer was of the d'Arsonval principle, formerly used at the Weather 

 Bureau and kindly loaned to me by the Eev. Jos6 Algu6, S. J. 



Series of test experiments were made when the apparatus was complete. 

 B was immersed in oil baths of different temperatures in one series, in another 

 it was inclosed in a tube fitted with a thermometer and immersed in water, 

 the temperature of which was varied. In a third series the temperature of 

 A was changed and that of B kept constant. Of course, all the wire connections, 

 the galvanometer, the scale, and the position of the telescope were kept unchanged. 

 One division of my tangential scale was equal to 0°.19 of the thermometer, and 

 half of this interval could be read exactly and quarter intervals approximated. 

 Readings were therefore correct to 0°.l. The deflection of the galvanometer 

 was directly proportional to the change in temperature if the temperature limits 

 were not greater than 8° or 9°, equal to about 40 parts on my scale. 



The second type of apparatus is shown in figure 3. One constantan wire and 

 one iron wire were soldered together. The place A was to be kept at constant 

 temperature, and B to serve as the thermo- 

 metric junction. Here the wires were ham- 

 mered to fine leaf and soldered together in the 

 form of a very flat V. They were insulated 

 by tape and covered with a layer of silk and 

 oilcloth. A was fixed on the mercury bulb M 

 of a thermometer T and inclosed in a tin 

 cylinder C so that the wires did not touch the 

 tin box C. Two copper wires I led from the 

 iron to the galvanometer, the places of junc- 

 tion between iron and copper being kept at 

 the same temperature. The tin box C was 

 placed in a Dewar vacuum-jacketed vessel of 

 about 300 cubic centimeters capacity, which was 

 filled with oil 0. The Dewar vessel, resting 

 on a piece of bamboo E, was placed in a large 

 glass jar F which was filled with carbon K. 

 The Dewar vessel was closed by a cork stopper 

 G, having holes for the thermometer and the 

 four wires. The carbon was covered by a 

 cylindric cardboard H, which latter was covered with cotton. The two wires 

 of constantan and iron in this drawing are shown shorter than in the apparatus, 

 the place B was freely movable and 1 meter distant from the jar F which was 

 kept under a large wooden box. The temperature of A was constant for one 

 hour or more at 0.01. Test experiments were performed for each apparatus at 

 varying intervals by placing B in oil baths of different temperatures. One 

 division of my galvanometer scale corresponded to 0°.423 on the thermometer in 

 the apparatus I used most, so that the sensitiveness of this thermocouple was 

 less than one-half of that used for measuring the skin temperatures. Thus, larger 

 temperature variations, accurate to 0°.2, could be recorded with this second type 

 of apparatus. 



A few words are necessary concerning the technique of taking the 

 skin temperature. Two persons must cooperate in making the measure- 

 ments, one reading the galvanometer, the other handling the thermo- 

 metric apparatus. The latter work was performed by a clever native 



Pia. 3. 



