TRANSACTIONS OF SECTION A. 657 
fiscated years ago by the Canadian Government, and by their permission I have 
converted it into an ‘air barometer.’ To effect this it was only necessary to place 
within its centre a four-inch tube extending from top to bottom, and to seal her- 
metically the large chamber with the exception of two small holes at the bottom of 
the central pipe. ‘Io complete this device water is poured into the central pipe until 
the confined air in the large chamber is sufficiently compressed to sustain a column 
of water in the central tube. Upon the water in the latter a float is placed and con~ 
nected to the recording pen on the right of the instrument in a similar manner to 
' the other as already described. Both carriages bearing the recording pens are 
mounted on small rollers which move on two horizontal and parallel brass rods. 
The effect of changes of atmospheric pressure upon this air barometer when increas- 
ing is to depress the column of water and float in the central tube, which causes 
an upward movement of the pen upon the paper; when the external pressure is 
reduced, a contrary movement occurs. In order to keep the temperature in the 
air chamber as constant as possible, the latter is deeply imbedded in sawdust. 
The recording sheet is 36 inches by 24; it is ruled one way for hours, half, and 
quarter hours, each being ‘25 of an inch apart. The tidal range of 10 feet occupies 
the lower portion, and is ruled for feet and every two tenths of a foot, the ratio 
of movement between the float and pen being 10 to 1. The remainder of the sheet 
is graduated into barometric tenths and every two hundredths of an inch, each tenth 
corresponding to 1:2 of an inch upon the paper. 
The object of this instrument is not so much to furnish a very accurate 
measurement of barometric changes as are now obtained from standard ones, as to 
magnify the movements to enable one to study the characteristic forms and amplitude 
of the ripples, waves, and billows which are now known to exist in our atmo- 
sphere during all conditions of weather. Although this instrument has only been 
in operation during the summer type of fine settled weather, numerous interesting 
forms of undulations have been recorded by both tidal and barometric pens. The 
former are Imown as ‘Secondary tidal undulations,’ and though the writer thinks 
these are due at all stations to atmospheric waves or billows travelling over the 
surface of the ocean, he is inclined to believe their relative amplitude and time 
interval vary according to the configuration, area, and depth of the semi-enclosed 
basins where they usually occur.' 
As previously observed upon the Great Lakes,? and along our Atlantic Coast, 
so also here, that when the water unduiations are most pronounced, so are the 
barometric ones, and as the latter become less disturbed so do those on the water. 
In order to increase the value of these records I made them up into monthly 
rolls, which form lengths of either 60 or 62 feet. Upon these are entered the hourly 
direction and velocity of the wind for Victoria, the hourly height of the Esquimalt 
tides as taken from its gauge, also the same from the Sand Heads which are situ- 
ated in the Gulf of Georgia near the mouth of the Fraser River. The curves for 
these are then drawn in, in red and blue pencil, as will be seen upon the accom- 
panying sheet, which not only graphically shows various primary tidal phenomena, 
but the marked secondary undulations upon the Victoria trace, and how these 
diminish as the barometric trace becomes less disturbed. 
It is the writer’s intention to continue this work for the following reasons: 
That, whereas the great winter storms that sweep over this Province approach 
from the Pacific, it is thought that their advent may be preceded by certain types- 
of barometric wayes and tidal secondaries, also by abnormal tidal elevations or 
depressions which are known to occur when great barometric differences prevail 
over the adjacent ocean though the local barometer may still be high. The tabu- 
lating of the exact times of high and low water will assist in checking the present 
American tidal predictions for our coast, which being based upon limited data are 
not invariably correct. As one of Professor Milne’s seismographs is now in most 
successful operation here, and frequently recording tremors and quakes, it is 
1 ¢ The Origin of Ocean Tidal Secondary Undulation,’ by F. Napier Denison, Can. 
Institute Proc. Read April 23, 1898. 
* «The Great Lakes as a Sensitive Barometer,’ by F, Napier Denison, Brit. Assoc. 
Report, 1897. 
1899. UU 
