INTRODUCTION 
15 
of the survey. Only in exceptional cases was it necessary to apply 
corrections to the soundings for a rise or fall of the surface during 
the sounding operations. 
Preparation of the Maps. — ^When the survey of a loch had been 
completed, the 6-inch Ordnance Survey map, with soundings laid 
down in position by the surveyors, and the sounding-book relating 
thereto, together with any special notes, were forwarded to the office 
in Edinburgh, where clean tracings on cloth were plotted, carefully 
compared with the soanding-book^ and contour-lines of depth drawn 
in at equal intervals. The areas within the consecutive contour-lines 
were then measured with the planimeter, and the volume of water 
contained in the loch, and the mean depth, calculated. The area 
draining into the loch was measured with the planimeter on the 1-inch 
Ordnance Survey map, and all particulars as to elevation, number of 
soundings taken, length, breadth, depth, area, and drainage area were 
entered in a large book ruled for the purpose. The tracings were then 
handed to Mr Bartholomew, who prepared copies on thin paper, 
with the printed names, etc., inserted in position. These were 
€arefully revised in the office, and then reduced by photography to 
half-size (i.e, to the scale of 3 inches to the mile) and transferred 
to stone, all the maps in these volumes being on that scale. After 
the publication of the printed maps the tracings on cloth were 
forwarded to the office of the Ordnance Survey for preservation and 
for future reference. 
Temperature Observations. — These were made in most of the 
lochs by means of Negretti & Zambra's deep-sea thermometers, 
which were immersed to different depths by the sounding-line and 
reversed by a messenger sent down the line. Different forms of 
frames and mechanisms for reversing the thermometers were ex- 
perimented with, and it was found that the Scottish frame with side 
lever, originally designed in connection with the work of the Granton 
Marine Station, was the most satisfactory (figs. 7 and 8).^ Several 
1 In fig. 7, F is the frame attached to sounding-line by the clamp V and the 
short spiral C. 
T, thermometer turning in frame on pivots jj. 
P, iron pin passing through holes at h h, and projecting into groove at top of 
thermometer case at G. 
L, lever, one end passing through a hole in P, the other forked to enclose 
sounding-line. 
S, spiral spring keeping lever down. 
B, messenger, which by its action on the lever raises pin P and inverts 
thermometer. 
/ is a catch which is caught by the tooth t on spring s when thermometer is 
inverted. 
B', messenger which is released by inversion of thermometer. 
Fig. 8 shows the construction of the messengers B and B'. 
