378 
MR. E. H, GRIFFITHS ON THE VALUE OF 
be remembered that any such change would at once produce an effect on the 
mercury, and, by its action on the regulator, reproduce the original condition. 
Section IV. —The Motor and its Connections. 
A belt passed from the motor to a vertical shaft fixed near the back of the tank. 
This shaft carried “ speed-wheels,” from which ran two cords, one to the stirrer in the 
outer tank, the other to the stirrer in the calorimeter. In order to prevent any 
“ slipping,” with which we were at one time much troubled, all these cords ran 
through loose pulleys hung by strings, which, passing over small fixed pulleys, were 
connected with pans containing shot. The tension of the cords could thus be regu¬ 
lated by altering the weight of shot, and any change in their length, due to 
stretching, &c., was of no consequence. The shaft of the calorimeter stirrer was 
connected with the revolving piece above it by a double Hooke’s joint. Until 
experiment J 19 a short piece of brass tubing with a cross wire at each end served 
as the Hooke’s joint, with the exception of J’s 17 and 18, when only a single 
Hooke’s joint was used. A difference in the “stirring supply” was shown in these 
two experiments (see p. 450), probably due to some difference in pressure between the 
agate cylinder at the bottom of the stirring-rod and the ring surrounding it. After 
experiment J 19 the connection was made by a small circle of thin wire, which 
passed through a hole in the revolving shaft and dropped into a slit in the top of the 
stirring-rod. Thus all rigidity in the connection was avoided, and the stirring effect 
was more regular after the change. Above the stirring-shaft was a Harding’s 
counter, whose axis carried at its upper extremity a V-pulley, and at its lower 
extremity the Hooke’s joint (see Plate 2 , fig. 2 ). These counters move in steps, and 
not wfith a continuous sliding motion, and, as it was essential that we should be able 
to read with considerable accuracy the time of each 1000 revolutions, this form of 
counter was the best adapted to the purpose. The wear that these instruments will 
stand is surprising, for, on many occasions, nearly a quarter of a million revolutions 
per day were recorded, and the same counter was used by us throughout our experi¬ 
ments of 1891 and 1892, with the exception of experiments J 20 to 34, when the 
original counter, having shown some slight signs of wear, was replaced by another. 
The motor (one of the fan type) was by Bailey and Co., and of the usual pattern. 
When working at the Sidney Laboratory in 1891, the changes in pressure, and there¬ 
fore in the speed of the motor, were so frequent that we w^ere compelled to relinquish 
our attempts to perform our J experiments during the day, and the observations had, 
therefore, to be taken between 10 p.m. and 2 a.m. Even during these hours, the 
regularity was far from satisfactory. 
As has been explained in the introduction a special room was built for the experi¬ 
ments of 1892. Here the supply pipe to the motor led directly from the main, but 
the irregularities of pressure were still so great as to render some improvement 
