112 EXPERIMENTS ON THE FROUDE. 
second so that from the beginning of one notch to the corresponding part 
of the next notch represents one half second. ‘To facilitate counting every 
fifteenth contact is omitted which gives the broad interval and these broad 
intervals correspond to eighths of a minute. The clock is also arranged to 
give quarter second contacts if desired but, as the half-second record can 
easily be read to tenths of a second, the shorter intervals were seldom used. 
BB is the record of the revolutions of the propeller shaft and for this 
the contacts were made from a toothed wheel which was operated by a 
ratchet and pawl which in turn were operated by a cam, on the main shaft. 
Every tenth tooth was omitted which makes the broad interval and facili- 
tates counting. Duplicate pens were provided for twin or triple screws and 
STAATING 
SIGNAL 
i TS IS RE es 
en Eee eee 
EE BASE LINE 
BB REVOLUTIONS 
RRR RRR I ERE lA R RE APPEAL PRLS NPS PPL 
AA Time 
Fic. 31. 
though not used on the Froude gave very interesting records on several 
trial trips of full sized ships. 
The record of the crossing signal is given at CC and for this a contact 
was pressed by hand on crossing the start and finish ranges. Counting the 
time interval on AA between these two signals gives the time on the course 
and therefore the speed. 
For the thrust of the propeller shaft, electrical contacts could not be 
used, as the motion of the scale beam lever had to be transferred directly 
to the tape. The major part of the thrust was taken up by the scale beam 
weight and a small spring was used to maintain the arm horizontal, thereby 
taking up the rest of the thrust. The deflection of this spring when magni- 
