8 



Mr. E. EL Griffiths. The Value of [Feb. 16, 



gas regulator of a novel form, which, controlled the supply of gas to a 

 large number of jets. Above those jets was placed a flat silver tube, 

 through which tap water was continually flowing into the tank, all 

 parts of which were maintained at an equal temperature by the rapid 

 rotation of a large screw, Thus, the calorimeter may be regarded as 

 suspended within a chamber placed in the bulb of a huge thermometer 

 — the mercury in that bulb weighing 70 lbs. A change of 1° C. in 

 the temperature of the tank Avater caused the mercury in the tubes of 

 the regulating apparatus to rise about 300 mm. Special arrange- 

 ments were made by which it was possible to set the apparatus so 

 that the walls surrounding the calorimeter could be maintained for 

 any length of time at any required temperature, from that of the tap 

 water (in summer about 13° C, in winter 3° C.) up to 40° C. or 50° C. 

 We know by observation that the temperature of the steel chamber 

 (when once adjusted) did not vary by 1/500° C, and we believe the 

 variations were much less. 



2. We experienced great difficulty in devising a suitable form of 

 stirrer ; and we attribute the failure of our earlier experiments to 

 defects in the ordinary forms. We find it impossible, without a 

 lengthy description, to give a clear idea of the stirrer ultimately 

 adopted. We can only state here that it was completely immersed 

 when the depth of the water exceeded 1 cm., that its bearings were 

 outside the steel chamber, and that the water was thrown from 

 the bottom to the lid of the calorimeter. 



More than 100 experiments w r ere performed (many of them last- 

 ing several hours) in order to determine the value of o + p (0i — 0q),* 

 when the calorimeter contained different masses of water. The 

 harmony amongst the results was satisfactory. 



These experiments proved that over our range of temperature, 

 (>+p(0i — O ) was a linear function of Oi — O , and Newton's law of 

 cooling appeared to hold strictly true over a range of 6° C. below 

 to 6° C. above the temperature of the surrounding walls, i.e., from 

 14° C. to 26° C. ; and our experimental results were of such a nature 

 that a very small departure would have been apparent.f 



We found that with our form of stirrer a = r z h where r was the 

 rate of revolution, and h some constant. This relation held true for 

 all values of r between 26 and 34 revolutions per second, and, as 

 during our J experiments we proposed to maintain a rate of as 

 nearly as possible 30 revolutions per second, we were able to make 

 the necessary correction for small deviations from the normal rate. 

 In order to diminish the irregularities in the motor, a special 



* a — rise in temperature per 1 second due to the stirring, p = gain or loss in 

 temperature per 1 second due to radiation, &c, when 0i — 9 o = 1° C. 



f If the temperatures were reckoned on the mercury thermometer scale, the 

 curvature would be considerable. 



