120 PHILOSOPHICAL TRANSACTIONS. [anNO 1704. 



excepting its outer rind or shell, which is properly called china china, and is 

 esteemed by the natives beyond the bark taken from the trunk or boughs.* 



Account of a new Baroscope. By Mr. Caswell, of Oxford, F. R. S. 



N°290, p. 1597. 

 Suppose ABCD, pi. 3, fig. 20, to be a bucket of water, in which is the baro- 

 scojje xrezyosm, consisting of a body xrsm, and a tube ezyo, both which are 

 concave cylinders communicating with each other, and made of tin, or rather 

 of glass ; the bottom of the tube zy has a lead-weight to sink it, so that the top 

 of the body may just swim even with the surface of the water, by the addition 

 of some grain-weights on the top. When the instrument is forced with its 

 mouth downwards, the water gets up into the tube to the height yu. On the 

 top there is added a small concave cylinder, which I call the pipe, to distinguish 

 it from the bottom small cylinder, which I call the tube ; this pipe is to sustain 

 the instrument from sinking to the bottom ; md'xs a wire ; ms, de are two threads 

 oblique to the surface of the water, which threads perform the office of dia- 

 gonals ; for while the instrument sinks more or less, by the alteration of the 

 gravity of the air, there, where the surface of the water cuts the thread, is 

 formed a small bubble, which ascends up the thread, while the mercury of the 

 common baroscope ascends. 



The circumference of the body is 21 inches, therefore its area = 35 : the 

 altitude w* = 4 ; therefore the solid content = 140; each base arm, rs, has a 

 convexity, whose altitude is .65, therefore the conoid on each base is nearly 

 = IH; hence d the whole body is = \A0 -\- Hi -h 1H= l63, and b the 

 entire altitude of the body = 4 -}- .65 -f- .65 = 5.3. The inner circumference 

 of the tube is 5.014, therefore its area n = 2; the length of the tube = 4.5, 

 therefore the tube's capacity = Q ; hence c, the content of the body and tube 

 = 163 + 9 = J 72 cubic inches, that is almost 24- quarts. 



Suppose the air's pressure when greatest = 30.5 inches of mercury = 30.5 

 X 14 = 427 of water, and /= 427 ; therefore fc = 73444. Put a for the 

 depth OM, of the air in the tube when the body is just all immersed ; the air in 

 the instrument on immersion contracts somewhat by the cold of the water ; 

 this contraction I find is nearly as much as would be produced by an addition of 

 I inch to the atmosphere's altitude 427 ; this in cold weather; but in warm wea- 

 ther, it is probably twice as much ; but we will now suppose it = 1 ; therefore 



• A more ample account of the Jesuits* or Peruvian bark occurs in the 40th vol. of these Trans- 

 actions. It is the cinchona officioalis^ Linn. See Lambert's Detcriptionj with plates, of the genus 

 •inchona, published in 1797. Also Rui» Flora Peruviaua. 



