366 Mr. Mageough's Method of mounting Thermometers. 



will trace on the paper all the changes in temperature occur- 

 ring through twelve or twenty-four hours. 



But, where nothing more is required, the highest and lowest 

 degrees of temperature happening in a given time may be 

 registered by the assistance of a couple ol fine slips of light 

 wood, or two bristles, poised on axles, the ends being brought 

 over the circular scale so as to come in contact with a catch 

 fixed on the tube. 



Let AB, fig. 1. represent a thermometer tube, containing 

 the mercury, and being marked at the boiling and freezing 



c\\ 



points. Such tubes are easily obtained at the opticians. Let 

 C be the centre of gravity when the mercury is at the freezing, 

 and c the centre of gravity when it is raised to the boiling- 

 point; S is the place of an axle fixed across the tube, and 

 resting in two hooks or rings, one of which is represented in 

 the figure at the termination of the wire PS. Suppose the 

 point S to be in a perpendicular to the axis of the tube, erected 

 at the point c ; then it is clear that when the mercury rises to 

 the boiling-mark, the centre of gravity moves into c, this point 

 will therefore get into the perpendicular to the horizon under 

 S, and put the tube AB into the horizontal position, as shown 

 in the figure. Again, when the mercury sinks to the freezing- 

 mark, the centre of gravity coming into C will cause that point 

 to get into the perpendicular under S, and put the tube into 

 the position A'B': the arch A A' through which the end of the 



tube 



