History of Mechanical Inventions, fyc. 159 



again appeared in 1812, it was observed by Mr Wright, the occupant of 

 the land, that not one cicada came out of the earth on that piece of ground 

 where he had cut the trees before they appeared in 1 795 ; but that on all 

 the rest of the land, wherever there was a stump, or a tree had stood, the 

 earth was full of holes made by the ascending cicadae. These facts are in 

 my mind a sufficient evidence that it is seventeen years between the lay- 

 ing of the egg, and the reappearance of the cicada. Through how many 

 transformations they pass, is to me unknown ; but from the length of time 

 they lie in the earth, it is probable the changes are more than one. But 

 that they do not travel far is evident, from their coming up immediately 

 by, or under the spot, where the tree stood in which the eggs were depo- 

 sited. — Prof. Silliman's Journal, No. xxii. p. 327. 



Art. XXVI.— HISTORY OF MECHANICAL INVENTIONS AND 

 OF PROCESSES AND MATERIALS USED IN THE FINE 

 AND USEFUL ARTS. 



The following important articles connected with the theory of the steam 

 engine have been kindly communicated by W. J. Henwood, Esq. Mem- 

 ber of the Zoological Society, and of the Royal Geological Society of Corn- 

 wall. They form the principal part of a small pamphlet just published for 

 circulation among the practical men in the mining districts of Cornwall. 



1. Observations on the Performance of the Engine at Huel Towan recently 

 \ erected by Mr Samuet. Grose.* 



The various forms of steam boilers have been very ably described by 

 Mr Taylor; from whose observations it appears that in some of those used 

 in Cornwall, the heated air, after having passed through the cylindrical 

 iron tube A, Plate II. Fig. 12, which is surrounded with water, and in 

 which the fire place is situated, returns through the flue B, which passes 

 horizontally underneath the boiler, to the end at which the fire is situated ; 

 here it divides, passing through CC into the flues DD, and through them 

 is conveyed along the sides of the boiler, and thence escapes to the chim- 

 ney, a a is the part of the boiler filled with water, and b is the reservoir 

 of steam. It will be observed that the upper parts of DD approach very 

 near to the surface of the water ; and as the heated air is carried so many 

 times round the boiler, it seems probable that but little heat is carried off 

 to the stack. I am not aware that the side flues were ever before carried 

 so near the water line, as above represented ; but this is the manner in 

 which they are now constructed at Huel Towan. There are very many 

 instances in which the air passes from A to DD, thence to B, and thither 

 to the chimney. The diameter of the cylinder of the engine, on the per- 



* Since the following article was written, this engine has been found to consume 

 fifty-four bushels of Swansea coal in 26 hours ; and its average performance for the 

 time was 87,2 millions of pounds, raised one foot high by the combustion of one 

 bushel of coals.— En. 



