TRANSACTIONS OF THE SECTIONS. 



25 



that the sounding-line in these attempts must be so carried away with the moving 

 strata of waters as to render the length of line run out a verj' imperfect indication of 

 the depth reached by the plummet. 



Dr. Scoresby next proceeded to communicate his plan for the determination of 

 surface-currents, and relatively of strata-currents. 



The ordinary mode of determining the set and velocity of currents — by the 

 differences betwixt a ship's position on each day's run as determined by celestial 

 observations and the "dead-reckoning" — is necessarilj' and obviously very uncertain, 

 often entirely delusive. None of the elements of the log and reckoning are or can 

 be correct ; the distance run, the compass course, the steerage of the ship, are all 

 more or less inaccurate. The author's own experience had afforded numerous 

 cases in practical navigation of great and remarkable differences betwixt the day's- 

 reckoning and celestial observations, such as might have been taken as indications of 

 currents of considerable influence, where, it was almost certain, the main differences 

 were really due to bad steering (when scudding or sailing with the wind on the beam 

 or quarter) ; to errors in the distances indicated by the log, or to peculiarities or 

 changes in the ship's local attraction. 



No doubt broad determinations as to great and decided currents, and proximate 

 results by means of multiplied observations on currents of moderate velocities, are 

 derivable from the ordinary process ; but for really satisfactory results, far more 

 accurate and conclusive processes need to be instituted. And it would be well 

 deserving of an enlightened government of a maritime country like ours to employ 

 some of their smaller war- vessels, and so to afford useful and instructive practice 

 to junior officers, in investigations concerning currents, and particularly strata- 

 currents. And for such investigations certain modes, Dr. Scoresby believed, might 

 be made easily available, calculated to yield much valuable and interesting informa- 

 tion on this important subject. 



Two leading processes were then described as appearing to be applicable to these 

 determinations : — 



1. The planting in particular positions in the ocean, from an attendant vessel, 

 buoys with flags, kept in their places by a resisting apparatus below the surface, 

 which may be denominated a airrent-measurer, and determining, after a night's 

 interval, for instance, the changes of their position from celestial observations. 



A convenient construction of the current-measurer, 

 with a view to portability of stowage, might be a double 

 oblong frame of iron, attached by a transverse pin as a 

 hinge, by the middle of each, so as to allow of their being 

 spread out as vanes in a vertical plane, or placed flat on 

 each other when not in use. These frames, which might 

 be 6 or 8 feet in length by 2 or 3 in breadth, being covered 

 with linen, would, when sunk in the water, as indicated 

 by the annexed figure, afford sufficient resistance, pro- 

 bably, for all the purposes contemplated. 



2. Placing, during a calm, a small boat in the water, 

 constructed for the purpose, light, and slightly resisting 

 of motion, with the current apparatus for the determination 

 of the relative set of strata-currents. — The current-mea- 

 surer, attached and suspended by a small wire run off a 

 reel fixed in the bow of the boat, might be let down to 

 various depths in succession, with a register-thermometer 

 attached at each new depth, when the motion of the boat 

 and its direction, as shown by the position of a surface- 

 float or buoy, would, after but short intervals of time, 

 indicate, proximately, the relative motions of the surface- 

 water and the water at the several depths of the resisting 

 apparatus below ; whilst the register-thermometers might 

 give useful information on the extremes of temperature of 

 the various sections of water passed through. 



By these arrangements information would be obtained as to the following 

 particulars : — 



By the surface-buoy (1) we should ascertain, if the weather were sufficiently calm. 



