16 



Captain Sabine's Experiments on the 



numbered 3, 4, 5, and 6, as being those from which the most 

 satisfactory conclusions can be drawn. 



In order to examine the effect of differences of temperature 

 on the time of vibration, I placed a bell-glass receiver within- 



?r 



side the box in which the needles vibrate, and fastened the silk, 

 by which they were suspended, to the top of the receiver, which 

 was perforated for that purpose. A thermometer was placed 

 withinside the receiver, as near the needle as the space required 

 for its vibration would permit. The box was then closed by 

 the usual thick plate of glass at the top. In the apparatus thus 

 arranged, a needle was first vibrated at the natural temperature 

 of summer, about 65°. The glass plate was then removed, the 

 space which is shaded in the wood-cut was filled with ice, and 

 the plate replaced. When it appeared by the thermometer that a 

 sufficient time had been allowed for the temperature withinside 

 the receiver to become steady, the needle was again vibrated. 

 On the following day, the experiment was repeated at the same 

 hour and in the inverse order, the needle being first vibrated in 

 the colder, and then in the warmer temperature. By this means, 

 the difference in the time of vibration was obtained, corresponding 

 to the usual summer heat of this country, and to more than 20° 

 below it. To ascertain the correction for higher temperatures, 

 the box was itself placed withinside a large garden-pot, sur- 

 mounted by a garden glass. The hole in the bottom of the 

 pot was enlarged, so that the flame of a spirit lamp entering the 

 aperture, heated the air contained in the space between the 

 box and the pot, and ultimately that contained within the box 

 itself. Each of the needles were then successively vibrated, 

 1st, at the usual summer temperature ; 2d, at temperatures 



