THE EXPERIMENTS OF 1834. 89 



in a given depth may be traced to the varying height of the wave, the mean height 

 in these experiments having been three or four inches. When the depth of the 

 cross-section of the channel varies, the velocity is nearly the mean of the velo- 

 cities due to the depths. For the more perfect determination of the laws of the 

 motion of waves, I have begun a series of experiments extending through a much 

 more extensive range of dimensions ; those made in 1834 having been almost ex- 

 clusively made in reference alone to their connection with the law of resistance. 



On Resistance and Immersion. — For the purpose of conducting the inquiries re- 

 garding the immersion of bodies moving at high velocities, and the resistance of 

 the fluid at these velocities, an experimental vessel was constructed, a very light 

 skiff, capable of containing four or six observers, with the apparatus of experi- 

 ment. The " skiff" was constructed of iron plates, extremely thin, and only 

 weighed 430 lbs. The length of the skiff was 31.25 feet, breadth 4 feet, and her 

 figure as given in Plate III. This vessel has been drawn by a highly-bred 

 horse, at a rate of more than 20 miles an hour. The skiff carried the following 

 apparatus. 



(1.) Two forms of the tube of Pitot P' V" V"\ Plate III. Fig. 5. P' being 

 the aperture exposed to the water, P' P" a long tube, separating into two branches 

 communicating by stop-cocks with P" P'", two vertical glass tubes carrying gra- 

 duated scales, one connected with the open tubes being graduated in inches and 

 decimals, zero being at the level of the fluid, to be used for low velocities, and the 

 other for higher velocities, graduating so as to indicate, by the compression of air 

 in a ball on the top of the tube, the height to which the water would have been 

 sustained in an open tube of unlimited length. The observations made with 

 Pitot' s tube do not in any respect vary from those given by others, and generally 

 received as correct. The tubes of Pitot were only useful as giving an index of 

 velocity of considerable extent, and giving variable indices of velocity cotempo- 

 raneous with the variations of moving force. The observations with the tubes 

 served to confirm those of the chronometers as indices of velocity. 



(2.) Gauges of Immersion. — Many modes have been attempted of determining 

 whether the immersion of a floating body in motion be variable or constant. Rods 

 have been applied vertically between the gunwale of the vessel and the surface 

 of the water, but the change of form caused by the currents of the fluid and its 

 waves have interfered with this method. Lines stretched above the vessel, so as 

 to measure the distance between the summit of the vessel and the fixed string in 

 the two states of motion and rest have indicated an elevation, but have not given 

 the means of distinguishing whether this elevation consisted of the fluid rising 

 along with the vessel, or the vessel emerging from the fluid, or both of these 

 causes united or modifying each other. The method I have used is this : into 

 apertures pierced in the bottom of the vessel glass-tubes, open at both ends, and 



VOL. XI V. PART I. M 



