190 ΐ REPORT—1850. 
and 1844, that the force in the Atlantic Ocean was 611 105. per square foot, while 
the corresponding average for six of the winter months was 2086 lbs., or three times 
as great as in summer. These observations he had communicated in 1845 to the 
Royal Society of Edinburgh, and they were printed in the twelfth volume of the 
Transactions of that body. 
The author then stated that the greatness of those results has excited surprise in 
almost all to whom they have been communicated, and positive doubts have been 
expressed by many as to the correctness of the indications. Three classes of facts 
essentially different from each other may be appealed to as proving that if the indi- 
cations of the dynamometer are incorrect, the error must be in defect and not in 
excess. The first fact to which reference was made, was the elevation of spray 
caused by waves meeting with an obstruction to their onward motion. Most per- 
“sons are familiar with the frontispiece representations of the Eddystone and Bell 
Rock Lighthouses during storms, which are attached to the descriptive accounts of 
the erection of those works ; and although some deduction may be allowed for the 
fancy of the artists, still there can be no doubt that they are in the main faithful 
representations of a natural phenomenon. On the 20th of November, 1827, ina 
heavy ground swell after a storm, solid water rose at the Bell Rock 106 feet above 
the level of the sea, irrespective of the depth of the trough of the wave. Such an 
elevation is due to a head of water of the same height. The force then which urges 
the lower courses of the Bell Rock must have been nearly 3 tons per square foot, 
while the highest indication of the marine dynamometer at the same place, since the 
observations were commenced, hardly equalled 14 ton. The second class of facts to 
which the author alluded was the fracture of materials of known strength. The 
instance adduced was a small harbour in Argyllshire, where, in order to preserve the 
tranquillity of the tide-basin, a contrivance called booms, well known in harbour 
architecture, had been resotred to. The booms are logs of timber, which are placed 
across the entrance to a harbour and fit into checks or grooves which are made in 
the masonry on either side. The booms, therefore, act as a temporary wall or 
barrier against the waves. The set of booms referred to have been in use for about 
five years, and in that time the waves have broken no less than four Memel logs, 
measuring each 1 foot square in the middle, and spanning an entrance of 20 feet. 
From the known strength of the material, it will be found that on these four occa- 
sions a force must have been exerted equivalent to the uniform distribution of a dead 
weight of 30 tons, or at the rate of 14 ton per square foot ; while the highest result 
that had been recorded at the same place during the short period that observations 
were made was about 14 fon per square foot*. 
The last class of effects to which the author alluded was the movement of heavy 
blocks of stone. The information derived from such observations was not so certain 
or satisfactory as from the other instances. The only record he could adduce was 
the movement of a block of stone weighing about 14 ton, to which a marine dynamo- 
meter had been bolted. The stone was turned upside down, and the dynamometer 
indicated a pressure of little more than one ton. 
The author then referred to the overturning of the Carr Rock Beacon by the sea 
in 1817 during a heavy gale, but stated that, as we do not know the manner in which 
waves act when encountering obstacles, it was impossible to calculate what force 
had in this instance been exerted. The part of the column which was overturned 
was 36 feet in height and 17 feet diameter at the base, the rock being so small as to 
preclude a greater diameter. The author then concluded by stating the following 
desiderata which he thought important :— 
lst. Continued observations so as to ascertain constants for the Atlantic and Ger- 
man Oceans and the Irish Sea. 
2nd. Relative forces of the same wave, both above high water and below low 
water levels. 
3rd. Relative forces of the same wave against vertical and sloping surfaces. 
* Since the above was written three other booms have been broken.—March 13, 1851. 
