No. 6. 



Span Level — Hessian Fly. 



201 



ever being injured by electricity." The sen- 

 timent is probably correct; but I wish to 

 caution my readers against the practical in- 

 ference which may be drawn from it, viz. — 

 that sixty feet is the distance to iDhich a good 

 rod will extend protection. "No such dis- 

 tance can be assigned, because it continually 

 varies from nothing up to an indefinite ex- 

 tent, as the intensity of the electric charge, 

 and other circumstances, vary." (Vol. 3, p. 

 75, 346.) 



The same writer says — " Bright surfaces 

 appear to attract the electric fluid with the 

 greatest force." Will Agricola please to in- 

 form me how and where I can observe such 

 an appearance. I know that such an opinion 

 prevails, but 1 have yet seen no appearance 

 to attest its truth. It remains to be my 

 opinion that " brightness is only necessary as 

 a security for sharpness." (Vol. 3, p. 76.) 



My readers are requested attentively to 

 peruse ' Observer,' No. 16, Vol. 3, p. 73, and 

 No. 18, p. 346, where much scientific and 

 practical information may be obtained. 



The Span Level lor Irrigating MeadoAvs. 



" At the level of the water where you be- 

 gin, drive a pin into the ground, on which one 

 leg of the level can rest, then bring the other 

 leg round, until it touches the ground on a 

 level with the top of the pin, and then drive 

 in another pin ; and, having adjusted the 

 level most perfectly, make use of this last 

 pin as a rest tor one foot of the level, turning 

 the other about, until you find the level in 

 the same way, and so proceed. Thus you 

 discover the precise direction that the water- 

 course should hold, without digging through 

 heights or filling up hollows. 



This is for the purpose of conducting wa- 

 ter perfectly level ; if declivity is to be given, 

 amounting to one-quarter or one-half an inch 

 or more in every twelve feet — which is the 

 span of the level — instead of wooden pins 

 make use of one pin of iron, havinjr inches, 

 halves and quarters marked on the side, from 

 the square top downward, and have a num- 

 ber of wooden pins cut neatly at the top, 

 quite smooth or square. After fixing the 

 iron pin quite level with the first, drive a 

 wooden pin into the ground close by it, 



making its head go one-quarter or one-half 

 inch lower than the top of the iron pin ; then, 

 pulling out the iron pin and employing the 

 wooden one as a rest for one of the legs of 

 the level, put the iron pin in again for the 

 other leg, and driving another wooden pin by 

 the side of it one-quarter or one-half an inch 

 below as before, take up the iron pin and pro- 

 ceed forward after the same manner, and the 

 canal will have the same uniform degree of 

 slope throughout its whole extent, and the 

 fall can be regulated to any assignable de- 

 gree." 



Hessian Fly. 



Discovery believed to have been made in 

 relation to the Hessiaii Fly. 



COMPILED FOR THE FAEMERS' CAEIXET, 

 BY BENJAMIN H. COATES, M. D. 



A PAPER presented to the American Philo- 

 sophical Society by Miss Margaretta H. Mor- 

 ris, of Germantown, and relating to the above- 

 mentioned subject, was subsequently ordered 

 by that body to be published in their Trans- 

 actions. As, however, some time will elapse 

 before the appearance of the number of the 

 Transactions which will contain her paper, 

 we have thought that we could better serve 

 the agricultural readers of the Cabinet by 

 extracting the information given in a journal 

 recently authorized by the Society to be pub- 

 lished by its Secretaries, in an abridged form 

 and of earlier appearance. In the "Proceed- 

 ings" just printed for November and Decem- 

 ber, 1840, we find the subject mentioned, in 

 some paragraphs of which we here subjoin a 

 copy. 



" The Committee, consisting; of Mr. Nuttall, Mr. Lea, 

 aiifl Dr. Coates, to whom was referred a communica- 

 tiou by Miss Margaretta H. Morris, on the CeciJomyia 

 Destructor ^r Hessian Fly, reported in favour of publi- 

 cation, which was ordered accordingly. 



"The Committee express the opinion, that should 

 the observations of Miss Morris be ultimately proved 

 correct, they will eventuate in considerable benefit to 

 the agricultural community, and, through it, to the 

 public. Miss Morris believes she lias established, that 

 the ovum of this destructive insect is deposited by the 

 parent in the seed of the wheat, and not, as previously 

 supposed, in the stalk or culm. She has watched the 

 progress of the animal since June, 1836, and has satis- 

 fied herself that she has frequently seen the larva with- 

 in the seed. She has also detected the larva, at various 

 stages of its progress, from the seed to between the 

 body of the stalkand the sheath of the leaves. In the 

 latter situation il passes into the pupa or 'flaxseed 

 state.' According to the observations of Miss Morris, 

 the recently hatched larva penetrates to the centre of 

 the straw, where it may be found of a pale greenish- 

 white semi-transparent appearance, in form somewhat 

 resembling a silk-worm. From one to six of these 

 have been found at various heights from the seed to the 

 third joint. They would seem to enter the pupa state 

 about the beginning of June. 



" This fly was not observed by Miss Morris to inhabit 

 any other plant than wheat. 



" To prevent the ravages of this destroyer of the 

 grain, it will be proper to obtain fresh seed from locali- 

 ties in which the fly has not made its appearance. By 

 this means the crop of the following year will be un- 



