I 



Marine Thermometer Case. 295 



lion, that I have taken the hberty of offering the instrument to 

 the notice and encouragement of your patriotic Society. 



I am. Sir, &c. &c. &c. 



• • RonERT Jamieson. 



Reference to the Engraving of Mr. Jamieson's Marine Ther- 

 mometer Case, Plate II. 

 Fig. 5 is an exterior view of the instrument, and fig. 3 is a 

 section of the same, with the inclosed thermometer. 



The general form of the case is that of a cylinder or tube of 

 copper, one-eighth of an inch in thickness, and seventeen inches 

 in length ; each end is open, and is bevelled off at the mouth for 

 the more free admission of water. 



V is the handle for the purpose of fixing it to the end of the 

 cord. This handle is moveable on two pivots, by means of which 

 it can readily be thrown on one side when it is necessary to take 

 out or put in the thermometer. 



At 2i inches from the top, is the circular joint o o, by means 

 of which the lid forms a water-tight joint with the body of the 

 case ; the lid is also furnished with a hinge, on which it may be 

 thrown back. 



The valves are placed at each extremity of the tube, the upper 

 one opening outwards, and the lower one inwards : they are com- 

 posed of the following parts : 



p q, a short cylinder or box, bevelled at each extremity. 

 s s,a. bridge or cross bar, bulging at the middle, and there 

 perforated, for the purpose of receiving an upright pin, to the 

 upper end of which is fixed the circular plate of the valve, and 

 to the lower end a screwed stud t, the round head of which pre- 

 vents the pin of the valve from being drawn, by the pressure of 

 the water, through the perforation in the cross 'bar. 



r r, a circular j)r()jection, on which the bottom of the thermo- 

 meter rests. 



From this description, it is obvious that when the case con- 

 taining the thermometer, and having its lid carefully closed, is 

 diopped into the sea with aline attached to the handle, it sinks 

 rapidly in nearly a vertical direction, and at the same time the 

 pressure of the water throws up both the valves. In consequence 

 of this, a current of water is constantly passing through the case 

 while the instrument continues to sink. As soon, however, as 

 by the check of the cord the instrutuent becomes stationar\^ the 

 valves fall into their places, and intercept the escape of the wa- 

 ter ; the quicker the cord is drawn up, the more completely are 

 the valves secured, and the influx of the upper water the more 

 perfectly prevented. As soon as the case comes to hand, the lid 

 i*; to be thrown back and the thermometer withdrawn just sutli- 

 ciently to enable the observer to read off the degree at which the 

 njercurv stands. 



