CLYDE SEA AREA. 5 



The glass-encased thermometer is fixed by means of thick indiarubber rings and 

 washers in a perforated brass case, and some observers have found that these rings tended 

 to make the instrument somewhat sluggish in its action. I only observed this effect on 

 two occasions when the rings had got displaced, and, blocking the perforations, checked the 

 flow of water between the brass tube and the bulb. On altering the position of the rings 

 there was no further trouble. 



There is no question as to the perfect suitability of the Negretti and Zambra ther- 

 mometer for all marine work where the exact temperature at a given position is required. 

 There is, however, considerable difference of opinion as to the best mechanism for insur- 

 ing inversion of the thermometer at the wished-for point. I have never used the original 

 wooden float with shot counterpoise, nor do I think that satisfactory results ever attended 

 its employment. Magnaghi's frame was a marked improvement. In it the thermometer 

 mounted on trunnions is held upright in the frame by a pin, which is raised by the action 

 of the rush of water past a screw propeller, on the instrument being drawn up. At first 

 there were two blades on the propeller, but the addition of a third gave it much greater 

 certainty in working. When the thermometer falls over, it is clamped by a side spring, 

 and retained in its inverted position until reset. A light indiarubber band passed round 

 the upper part of the frame insures that the reversal takes place immediately on the pin 

 being withdrawn. The Magnaghi frame in its original form, and with the addition of 

 many modifications, has been largely used for deep-sea work, and has given considerable 

 satisfaction. The work of the Scottish Marine Station in shallow water and amongst rapid 

 currents soon revealed a number of defects. When the screw was arranged so as to reverse 

 the thermometer when hauled up through less than one fathom, it was often set off by the 

 pitching of the ship or by the force of the current ; and when adjusted for a longer haul, 

 the exact depth at which the instrument turned over could not be ascertained, and it was 

 impossible to get bottom temperatures. The method of attachment to the sounding-line 

 by lashings was also found to be troublesome and slow, especially in cold and wet weather. 

 The Scottish frame was accordingly devised. It is a modification of Magnaghi's, the 

 screw pin with its revolving gear being replaced by a simple pin actuated by a lever, 

 which is depressed by a weight or " messenger " slipped down the line, striking on the 

 forked outer branch. A vice-clamp serves to fix the frame to the sounding-line at any 

 point, and with great rapidity. The final form of frame was not arrived at until after 

 many experiments, but thousands of observations have shown it to be convenient and 

 trustworthy. The form which was found most convenient is figured in Plate L, and 

 a sufficient description is attached to show the object of the various parts. An improved 

 form of clamp to secure the instrument when reversed has been introduced by Messrs 

 Negretti and Zambra, and is smoother in action than that shown in the figure. 



Rung's extremely ingenious messengers, made in two pieces, which can be fitted 

 together on any part of the line, are used for the Scottish frame. 



The importance of having thermometers -which can be made to register at an}^ given 

 depth is very great. For instance, the temperature of the surface at Clapochlar, Loch 



