182 ROYAL SOCIETY OF CANADA 



fully selected points or stations; and to make use of the steamer itself 

 as a fixed point from wluch the speed and direction of the current can 

 be ascertained and measured. It is not too much to say that with ade- 

 quate appliances, as much information can thus be obtained in 24 hours 

 as in a week by running courses. This is emphasized in foggy regions, 

 for with a steamer at anchor, the fog does not interfere with the work. 



The direction of the current is obtained by means of a float at- 

 tached by a line to the stern of the steamer. It is built of board, and 

 weighted to bring its surface awash with the water. It is thus unaf- 

 fected by the wind. At night it is illuminated by a small electric light, 

 operated from a battery. 



The speed of the current is measured by a current meter, register- 

 ing electrically on board, and read every half hour, day and night. The 

 meter is lowered to the standard depth of 18 feet (three fathoms) which 

 is well below the keel of the surveying steamer, thus avoiding any error 

 in measurement when the vessel is held by the wind at an angle to the 

 direction of the current. Its suspension is specially arranged to obviate 

 error from rolling. 



The Under- current. — The investigtition of tlie under-current is of 

 the first importance in relation to wind disturbance ; as the wind neces- 

 sarily influences the surface of the water first, whereas the under-current 

 will continue to run in accordance with the tidal streams or the general 

 set, or whatever may be the normal conditions of the locality. It will 

 also come up to the surface as soon as the disturbing influences, v.'hich 

 have been acting on the surface of the water, cease to operate. It does 

 not appear that wind disturbance can extend to a greater depth than 8 

 or 10 fathoms at the most, under the influence of any gales that occur 

 in the summer season. A comparison of the surface current with the 

 under-current thus holds the first place as a method of detecting wind 

 disturbance. Otherwise, a comparison must be made with the normal 

 conditions, or tidal periods, deduced from observations in fine weather. 



The observations chiefly required, are the direction of the under- 

 current, and the time of slack water below, relatively to the surface 

 current. For these purposes a fan is used which is made of two sheets 

 of galvanized iron passing through each other at right angles; which can 

 be lowered to any desired depth by means of patent sounding wire by 

 which it is suspended. The depth is conveniently read on the dial of a 

 patent sounding machine. The fan is 26 inches deep and 18 inches wide, 

 and weighs 16 pounds. In stronger currents an additional weight is 

 attached, bringing the total weight to 27 pounds. The inclination of 

 the supporting wire from the vertical also gives a close estimate of the 



