14 THK FRESH- WATER LOCHS OF SCOTLAND 
were sent in 1905 to Lieutenant Robert Peary for use in his Arctic 
expeditions across the polar ice. 
Methods of Determining Positions of Soundings. — At the 
outset much time was spent in trials as to the best method of deter- 
mining the positions of the soundings : — 1 , by the sextant from the 
boat ; 2, by signals from the boat, when a sounding was taken, to 
observers on the shore ; and 3, by running lines with two poles placed 
one behind the other on shore. All these methods took a great deal 
of time, and the fixing of the position was complicated by the drifting 
of the boat with both wind and water currents. After repeated trials 
and a comparison of results, it was found that the most accurate 
method was to take the soundings as quickly as possible while rowing 
across the lochs from one point to another. Before making a section 
across a loch, the boatman was trained for some time to ascertain the 
distance covered in ten, fifteen, twenty, and fifty strokes with the 
oars. It was usual to row from a definite point on one side of the 
loch to a definite point on the other side, keeping objects one behind 
another in line. The distance between these two points was ascer- 
tained from the 6-inch Ordnance Survey maps, M^hich were throughout 
used for plotting the position of the soundings. The soundings were 
taken, say, every thirty strokes of the oars, and the total number of 
soundings was placed equally along the line, thus distributing any 
errors. This method was found to be extremely accurate for long, 
narrow lochs ; it is less correct in wide lakes without islands. Fre- 
quently the position of soundings near shore was ascertained by 
measurement with tape-lines or cords, several hundred feet in length, 
stretched from the shore. In addition to cross lines, soundings were 
usually taken in several positions between the lines. When any 
special features were indicated by the soundings, several series were 
taken radially from a fixed point. ^ 
The level of the surfaces of the lochs at the time of sounding was 
obtained by measurement with a surveyor's level and staffs to the 
bench-marks along the shores of the lochs. In the case of lochs at a 
high altitude it was frequently not possible to refer the surface to a 
bench-mark by levelling, owing to the great distance, and the spot 
levels were unsatisfactory. However, special Lake Survey marks were 
placed along the shore, showing the height of the surface at the time 
1 For the jDurpose of maintaining position in running lines of soundings across a 
loch, mirrors of alignment of different forms were used— one supplied by Chabaud 
of Paris from the designs of Professor Thoulet ; by means of these mirrors an 
object on shore hehind the surveyor is kept in line with another object on shore in 
front of the surveyor. 
2 A surveyor's dumpy level and figured staff, as well as small Abney levels, 
were used for this purpose. 
