36 Mr Foggo on the Dew-Point Hygrometer, 



marine and fresh water Molluscae are frequently found cover- 

 ed, the first, not only with sea plants, but with lepades and 

 serpulae, and the second, with its coating of vegetable green, 

 without either of these impeding the necessary motions, or 

 disturbing the vital functions of the contained animals. But 

 none of these instances apply to the case of Dr MitchilPs in- 

 sects, where the growth is from a part of the body that must 

 necessarily preclude the animal from exercising the functions 

 essential to life; and the size and weight of the productions 

 are besides such as to root it permanently to the spot. The 

 presumption to be drawn from analogous facts seems rather to 

 heighten the value of the proof which has been afforded by 

 observation, that the death of the insect must have taken place 

 prior to the commencement of the fungous vegetation. 



" Des personnes peu eclairees" (says an eminent naturalist 

 when writing on the same subject) " en ont voulu conclure que 

 des animaux pouvoient se transformer immediatement en ve- 

 getaux ; mais Ton sait que telle est la nature de certains 

 champignons, notamment de cette clavaire, de ne pouvoir 

 croitre que sur des substances animales determinees. Si le 

 temps n'est pas favorable, il perit plusieurs de ces nymphes 

 de cigales qui vivent dans la terre, sous les feuilles mortes. 

 La semence de la clavaire s'y attache et s'y developpe ; voila 

 tout le merveilleux." * 



Art VI. — On the Dew-Point Hygrometer formerly described 

 in this Journal^ vol. iv. p. 127. By Mr John Foggo, Junr. 

 Communicated by the Author. 



I HAVE inserted in a former Number of this work a brief no- 

 tice of a method of taking the dew-point by means of a simple 

 thermometer. Since that notice was published, I have had 

 occasion to give a very extensive trial to this method, the re- 

 sult of which has satisfied me of the accuracy and facility with 

 which observations may be made with it. Its utility has, how- 

 ever, been strenuously denied by an authority so high as that of 

 Mr Daniell ; and in replying to his objections, I shall embrace 



• Bosc, in Nouv. Diet. d'Hist. Nat, toin. xxi. p. 445. 



