421 
1910-11.] A Modified Form of Atwood’s Machine. 
The weight of the two pans and string used in the following experiments 
was 87’5 g, while additional loads of 50, 100, 150, and 200 g were added to 
each side. In each case two driving weights were tried, viz. 10 g and 20 g. 
The chronograph clock was carefully calibrated, giving a mean nominal 
second equivalent to R995 true seconds. 
The maximum fall available was about 700 cm., but although records 
were obtained for the complete fall in every case, the s — t 2 curves showed 
some curvature for the last few metres 'of fall, and in the case of large 
acceleration this curvature was quite pronounced, the acceleration in every 
case diminishing as the speed increased. This is obviously due to the re- 
sistance of the pans to motion through the air, and, in fact, the apparatus is 
used chiefly for the determination of these resistances with larger surfaces. 
The resistance was allowed for in the present experiments by using for the 
determination of a only the first part of the fall, where the speed was low 
and the graph was accurately straight ; should it be desired to use it over 
greater distances, it would be well to dispense entirely with pans, and to use 
weights made in the form of rods, so that the area presented normally to 
the direction of motion would be a minimum. 
4. Results. 
The following are eight different values of g obtained by the method in- 
dicated above. The experiments are grouped in pairs, at the beginning and 
end of which a was determined a few times, the mean of each set being 
taken as holding for the actual experiments. 
Values of g determined with Modified Form of Atwood’s Machine. 
2L 
(gram). 
a! 
(cm/sec 2 ). 
w 
(gram). 
2L + w 
(gram). 
2L + w + P- 9 
V 2 
(gram). 
a 
(cm/sec 2 ). 
9 
(cm/sec 2 ). 
187-5 
3-49 
10 
197-5 
218 
41-37 
978 
20 
207-5 
228 
82-00 
975 
...976 
287-5 
3-64 
10 
297-5 
318 
27-16 
979 
20 
307-5 
328 
56-19 
981 
...980 
387-5 
3-56 
10 
397-5 
418 
19-96 
983 
20 
407-5 
428 
42-35 
983 
...983 
487-5 
3-31 
10 
497-5 
518 
15-65 
982 
' 
20 
507-5 
528 
33 75 
978 
...980 
Mean value of <7 . . . . 
980 
