[October, 
624 Correspondence . 
The same author shows also that burning-glasses have been 
known from time immemorial, and are mentioned in the 
“ Clouds ” of Aristophanes, whilst a plano-convex lens has 
actually been found in the Ruins of Nineveh. 
M. De Rochas, in an earlier portion of the same volume of 
“ La Nature,” mentions also that fire-engines were known to 
Hero of Alexandria, and were described by him clearly in his 
“ Pneumatika.” They were improved, according to Vitruvius, 
by Ctesibius, and were hence known as the Ctesibian machines. 
In the Dark Ages they were lost sight of, and were re-invented 
at Augsburg early in the sixteenth century. 
Now, Sir, I would not have troubled you with a mention of 
these facfts were they merely historical curiosities ; but they 
seem to me instructive. They prove that useful arts and prac- 
tical inventions, and perhaps a body of Science from which they 
were derived, may be lost sight of and afterwards may be re- 
invented. Hence it is at least possible that arts may have once 
flourished which have been forgotten, but have not been reco- 
vered. In any case it is certain that the career of mankind has 
not been one of unbroken “ progress.” 
I may venture, further, to suggest that the occult knowledge 
claimed by certain mystics may be simply a more or less frag- 
mentary relic of what was once commonly known. Have we 
not in the above, too, a natural explanation of the miraculous 
“ fire from heaven ” which occurs in the mythologies of various 
nations ? — I am, &c., 
A Lucretian. 
INJURIOUS INSECTS. 
To the Editor of the Journal of Science. 
Sir, — I was much surprised to find, a few days ago, the folllowing 
assertions in a widely-circulated paper: — “Wherever these 
troublesome pests [apparently house-flies] abound we may 
always find consolation in the knowledge that they absorb im- 
purities which would otherwise cause far more serious incon- 
veniences than any that can be fairly ascribed to the buzzing 
restless little pests themselves.” 
Again, in the same leaderette is to be read — “ If the daddy- 
longlegs cannot give so good an account of himself as this, he 
can at all events defy the breath of slander to sully the harmless 
reputation of his brief existence.” (! !) 
