182 Hydraulic Investigations, 



to the limits 29-56 and 29*96, which is inconsistent with 

 observation. 



I will conclude this long letter by the bare relation of the 

 following experiment, which was made in a room where a 

 fire is kept in winter. — February 21, 1809, De Luc's hy- 

 grometer stood at 52°, the thermometer at 50°, and the ba- 

 rometer 29*88 inches. It is proper to remark here, that the 

 force of the permanent gases at Middleshaw cannot exceed 

 29*22 inches by the hypothesis, and must be considerably 

 less by observation ; consequently the pressure or' the va- 

 pour was greater than '66 of an inch. A silver vessel con- 

 taining a quart or more had been placed near the thermo- 

 meter at the commencement of the experiment, which be- 

 came covered with a very thin film of dew when cooled 

 down to 40°. I am, &c, 



John Gough. 



XXXII. Hydraulic Investigations, subservient loan intended 

 Croonian Lecture on the Motion of the Blood, By Thos. 

 Young, M.D, For. Sec. R.S. 



[Concluded from p. 133.] 



III. Of the Propagation of an Impulse through an elastic Tube, 



JL he same reasoning that is employed for determining the 

 •velocity of an impulse, transmitted through an elastic solid 

 or fluid body, is also applicable to the case of an incom- 

 pressible fluid contained in an elastic pipe • the magnitude 

 of the modulus being properly determined, according to the 

 excess of pressure which any additional tension of the pipe 

 is capable of producing ; its height being such, as to produce 

 a tension, which is to any small increase of tension pro- 

 duced by the approach of two sections of the fluid in the 

 pipe, as their distance to its decrement : for in this case the 

 forces concerned are precisely similar to those which are em- 

 ployed in the transmission of an impulse through a column 

 of air enclosed in a tube, or through an elastic solid. Jf the 

 i>ature of the pipe be such, that its elastic force varies as the 



excess 



