382 Hydrometrical Observations. 
In the specimen No. 6, I exhibit the tongue of an ox prepared after 
the method of Malpighi, and l.ere is certainly displayed a magnificent, 
but wholly artificial, net-work. In specimen No. 7, is shewn the tongue 
of a calf, prepared according to the mcthod I have recommended, and 
the mucous body exhibits the appearance so often already described. 
Specimen No. 7 exhibits the continuous layer on its external aspect. Spe- 
cimen No. 8, prepared from the tongue of an ox, shews this same layer 
on its internal aspect. Finally, in specimen No. 9, the dermis, continu- 
ous mucous body, and epidermis, are exhibited in the tongue of the 
sheep. 
Hydrometrical Observations. By Davin Stevenson, Esq. © 
Civil Engineer.* 
Velocities of Currents——For the purpose of ascertaining the surface 
velocities of currents, various methods may be employed. 
The most common, but by no means the most satisfactory, mode of 
proceeding, is to throw into the water a float composed of some small 
body (whose specific gravity is merely great enough to sink it to a level 
with the surface), at a point about 30 or 40 feet above the line of sec- 
tion, so as to insure its acquiring the full velocity of the current before it 
reaches the cord. An observer, stationed at the cord, notes exactly the 
moment at which the float passes, and follows it down the stream till he 
reaches the line of two poles, which have been fixed in reference to the 
observations, when he again notes the exact moment of its transit at the 
lower station. The elapsed time between the two transits is then noted 
in the book, along with the distance between the two places of observa- 
tion, which, owing to the irregularity of most rivers, with regard to 
width, depth, and velocity, can seldom be got to exceed 100 feet. This 
operation has, of course, to be repeated for every compartment of the 
cross section. 
Certain disadvantages attend this method, which render it not gene- 
rally applicable. For example, it is only adapted to rivers of limited 
breadth, owing to the impossibility of an observer being able to discover 
with sufficient accuracy when the float passes the station lines, if it be 
viewed from a distance, as from the bank of a broad river. There are, 
however, greater objections than this, which, when pointed out, will be 
sufficiently obvious to every one. In any part of the river passed over 
by the floats, the slightest irregularity of the bottom produces a disturb- 
* The interesting observations and experiments in this article are taken from 
a valuable work just published, and which we recommend to the particular atten- 
tion of engineers, viz.— A Treatise on the application of Marine Surveying and 
Ilydrometry to the practice of Civil Engineering, by D. Stevenson, Civil Engi- 
neer, and author of a Sketch of Civil Engineering in America, &e. 1 vol. royal 
octavo, with numerous plates and plans, &e. Adam and Charles Black, Edin- 
burgh ; Longman & Co., and L. Weale, London. 1842.” 
