392 Scientific Intelligence. [May, 
While hydrodynamical science remains in its present imperfect 
state, there sercly cannot be a want of subjects. -” 
There are many mechanical men who know enough of science 
to apply the discoveries of mathematicians, and also to direct 
their attention to proper objects. But, unfortunately, the works 
to which I allude refuse to insert any question without the solu- 
tion accompanies it. Hence useful subjects never come before 
their correspondents. An engineer might, without much diffi- 
culty, furnish them two or three hundred, all more or less useful 
in his profession ; and I believe most of them might either be 
correctly solved, or approximate answers might be obtained near 
enough for practice. And surely the editors of such works must 
always be competent judges of what is fit for insertion without 
the caution of having the solution with the question; and they 
certainly would have a better opportunity of selection were this 
restriction removed. 
Being shut out by the absurd restriction above noticed, I solicit 
a place for the inquiry below in your Annals, and not without a 
hope that there’ will speedily arrive a time when the present 
method of conducting mathematical works will be done away, | 
and free scope will be given to a spirit of inquiry that will call 
the powers of science into a new field of action, more honourable 
to itself and to the enterprising minds of my countrymen. 
Question.—What should be the thickness of a rectangular 
demirevetment so that it may be in equilibrio with the pressure 
of the earth, the earthen scarp above it making an angle of 45° 
with the horizon, and*the revetment itself vertical ? 
In this sketch a is the re- b 
vetment wall, and 6 the 
earthern scarp. The expe- 
riments of Col. Pasley prove 
that the common rules are 
not correct.* And it is ne- 
cessary that every circum- 
stance affecting the pressure 
of the earth be included ; because the engineer, knowing the 
conditions of equilibrium, can better determine what will be 
necessary forsecurity. Iam, Sir, your obedient servant, 
MAsonicus. 
XVII. Death of Hornemann. 
Baron von Zach has published an account of the death of 
Frederick Hornemann, a native of Hildesheim, in Lower Saxony, 
who was sent by the African Association in 1797 to explore the 
interior of Africa. Many of my readers will recollect the inter- 
esting papers published by the African Association from this 
enterprising traveller, and the sanguine hopes that were enter- 
tained that he would be able.to penetrate to Tombuctoo. These 
5 
* Course of Military Instruction, vol. iii. — 
