1887.] of the Surface Sea-ivater at the Sandheads. 21 



which can only be guessed at, if read to less than the nearest "002, 

 but, if so, what an amount of really valuable information may be got out 

 of an instrument, which, although a rough and rude one, is so much more 

 exact : the one is as different from the other as was the old cross staff of 

 Christopher Columbus' time from the double reflecting sextant of to-day. 

 Our forefathers were content to find their vessel's position to the nearest 

 two or three miles, but modern navigators are not satisfied unless they 

 get it to the fraction of a mile. 



Doubtless, the energy which brings the waters up from the ever- 

 frigid bed of the deep sea : — the energy of attraction and repulsion ; — of 

 contraction and expansion, or, of deadweight and buoyancy : — this energy 

 of motion, under different states and circumstances, of the chemi- 

 cally suspended salt atoms, contained in each ocean drop, will yet 

 be made to divulge its partially hidden and secret treasures to the prac- 

 tical scientist for the navigator's benefit : as has been the case with the 

 latent energy of that other heat vehicle and prime motor of the hurricane 

 blast, as well as of the gentle zephyr — the invisible water- vapour glo- 

 bule in the air strata aloft. All that is required is the aid of willing work- 

 ers and their faithful records : for all the facts as set forth above, meagre 

 as have been the opportunities for observing them, go far to prove that 

 the hydrometer, when constructed to show minute aggregation, or segra- 

 tion of salt atoms in the water, must prove to be no mean aid to the 

 sailor, more especially to the coasting navigator, since it is near coasts 

 that the currents generally are more capricious, or disguised by others 

 which have never been properly explained. It will aid him either as a 

 monitor of his vessel's proximity to land ; of her being caught in the 

 toils of some abnormal current, which may be hurrying his vessel on to 

 her destruction (as was nearly the case during the cyclone in the Bay of 

 the 19th, 20th, 21st and 22nd of November last, with the ship " Airlie :" 

 which vessel was found to have been driven by the storm-impelled cur- 

 rent 140 miles to the N. W., out of her dead reckoning, right through the 

 dangerous South Preparis Channel, and actually had an oyster shell 

 washed up on to her deck) ; or its indications may be made even to 

 warn the watchful shipmaster of the on-coming, though yet distant, 

 cyclone ; let alone its probable use to scientists, in more ways than one. 



My instrument, a rather large soda-water bottle, when ballasted, 

 or weighted, so as just to float with its wire pedestal (or support and cup 

 or pan for weights) in water at a temperature of 95° (which is the 

 warmest of any sea water), happens to have a fluid displacement, or, 

 which is the same thing, weighs in air exactly 10,000 grains — a con- 

 venient figure for calculating the several counterbalancing weights by. 

 The weights are made by dividing and subdividing 320 grains weight 



