John Young Buchanan

“ A great amount of ingenuity has been displayed in the invention of machines for registering the actual temperature of the water at any given depth, independently of that of the water above it, all of which require some assistance from the observer in bringing about a catastrophe which shall leave its mark on the condition of the instrument. ”

“ An apparatus which the author has devised for sounding the Scottish lakes, and found to act well, consists of a straight brass tube an inch in diameter, carrying a shoulder about one foot from the lower end. A cylindrical leaden sinker of suitable weight is slipped over the upper end, and rests on the shoulder. The line is made fast to an eye at the top of the tube, and the part of the tube below the shoulder can be unscrewed, and the mud which it has brought up squeezed out. The tubes bury themselves readily in soft mud and clay, and bring up considerable samples. ”

“ It is evident that, as the instrument descends and the air in it is compressed, the water forces its way in through an orifice, and past the spout. This spout is so formed that it delivers the water against the walls of the tube, down which it runs, and collects at the bottom. When the motion of ascent begins, the air, by its elasticity, tends to recover its original volume, and expands in the direction of greatest freedom. ”

“ A more real but exaggerated objection to the trustworthiness of deep soundings is founded on the existence of currents likely to cause deviations in the direction of the line, and to change the position of the ship. There is no doubt concerning surface-currents; they are observed and measured every day, and form an important factor in the navigator's daily reckoning. ”

“ All the self-registering thermometers are liable to error from the effects of pressure, which may amount to five or six hundred atmospheres on the outside of the instrument, while inside it is never greater than was that of the atmosphere when the tube was sealed up. Attempts to obviate them have been made by placing the thermometers or their bulbs in protecting inclosures, and by the device of leaving the instrument open at one end. ”

“ The deepest water, five thousand fathoms, is not subject to a pressure that can raise its density as much as one-twentieth part. Moreover, the weight of lead is increased by pressure much faster than that of water, so that, however dense the water may be, it would have to encounter a still denser lead. ”

“ Bottom temperatures may be measured by common thermometers protected so as to be uninfluenced in coming up through the warmer upper strata of water, by bringing the water to the surface and taking its temperature, or by self-registering thermometers, such as Cavendish's and Six's. ”

“ No one instrument, however, fulfills all the conditions required of a perfect deep-sea thermometer, and the investigator must use his judgment in selecting the one or more best suited to his particular purpose. ”