129 [ 175 ] 



4th. It revives the silkworms, gently stimulating them, because it 

 iS composed in a great measure of pure, vital air. 



5th. The vapor is not alone favorable to the health of the silkworms, 

 but influences the goodness of the cocoon.* 



Of the Hygrometer. 



Scientific men have invented various instruments fitted to measure 

 the quantity of moisture which the air may contain in any circum- 

 stances, using, in their construction, bodies which attract the dampness 

 from the air easily, and stretch by degrees, and which contract again 

 when the air is dry. A plate of common table salt, coarsely pounded, 

 may answer to show the moisture or dryness of the air. Hygrome- 

 ters of various materials have been constructed. The annexed cut, 



will give a good idea of a useful, sim- 

 ' -^*^ pie, and cheap one. The principle 



upon which it is constructed, maybe 



^ thus briefly illustrated. The efiect 



^* — — which a moist atmosphere has on any 



twisted cord, is that of diminishing 

 its length, by causing the spirals to 

 approach each other. If, therefore, 

 a long piece of string be attached to 

 the peg at B, and conveyed round the 

 pulleys C, D, E, F, G, with a weight 

 .suspended beneath, we may, by referring to the index hand and scale, 

 readily ascertain the amount of moisture that has been absorbed by the 

 vegetable fibre. If the string be soaked in a solution of common salt 

 in water, it will more readily indicate any slight accession of humidity 

 in the atmosphere, t 



It would be desirable to have two hygrometers in a large laboratory, 

 placed within a certain distance of each other, to ascertain the various 

 degrees of moisture in difierent parts of the laboratory. 



* So much importance is attached to the use of tlie acid fumigations by Dandolo, 

 and others, that it has been thought right, to retain his directions respecting them; 

 but it is proper to remark, that Mr. Nysten, after a course of laborious experiments 

 with them, and with other fumigations, comes to the decided conclusion, that they 

 are totally inefficacious as means of curing the actual diseases of silkworms. He even 

 found, in an experiment with two thousand sick worms, that more died in a room 

 where the fumigations were continually used, than in another, in which the pure air 

 was allowed to circulate freely among a similar number. He allows, however, that tlie 

 fumigations may act as a preventive remedy, by neutralizing" the bad air of the apart- 

 ment. It is with this view that Dandolo uses it. He confirms the repealed posi- 

 tions of Dandolo, and the experience of all practical writers and cultivators, that to 

 prevent the diseases of silkvvorms, it is only necessary to hatch the eggs in a regular- 

 ly increased heat, to feed the Worms with good and dry leaves, to keep them in a 

 pure air of t!ic temperature prescribed above, and, fuiallj', to observe rigid cleanli- 

 ness. Tie remarks that, it was not Paroletti who first used acid fumigations for 

 worms, but RlgaudTle Lille, who says that he thereby diminished the mortality among 

 1hem; but candidly acknowledges, that he freely admitted the external air at the 

 same time. — Nysten sur la Maladies des Vers a Sole, pp. 101, 103. 



fT. WiTliarTTs. The Scientific Gazette, part 3d, p. 81. London. 182.' 

 17 



