C 98 ] 
in thermometro Suecano, mercurio vivo impleto, 
frigus numero infra pundtum congeiationis aquae, quod 
in nive colliquefcente determinatur. (Quivis gradus 
eft pars centelima diftantke pundtorum congeiationis 
et ebullitionis aquae). Fricui dein pod quarundam 
horarum l'patium, fed nonnifi valde debilem eledtri- 
citatem elicere potui. Haec itaque iterum repofui, non- 
dum fatis frigefada putans, et mane fequenti, dum 
interea mercurius in thermometro quofdam gradus 
defcenderat, in camera non calefada tentavi, fed ad- 
huc minori fucceflu. Unum igitur fruftulum calefeci 
\ fperans hoc ipfo omnem vim eradicari; fed inopinato 
non modo non deflrudam inveni difpofitionem elec- 
tricam, fed valde audam. Idem mox repetii cum 
reliquis omnibus, codemque Temper effedu prima ten- 
tamina fada funt cum cryftallis objeda duplicantibus, 
quae in Suecia erant colledae : fufpicio igitur mihi inci- 
dit has inter et revera Iflandicas effentialem effe diffe- 
rentiam ; itaque comparavi in Iilandia natas, fed eadem 
monftrarunt phaenomena *. 
Ex hifce tentaminibus cum domini Delaval colla- 
tis fequi videtur, diverfas hujus cryftalli dari fpecies, 
quae eo diligentius examinand#, cum hucufque mine- 
ralogi non nifi unicam diftinguant. 
• • 
* Mr. Delaval had already obferved, in the letter here referred to 
by Mr. Bergman, that the property, in Iceland Cryftal, of lofing 
its ele&ricity by a moderate heat, was not common to all kinds 
of it : and mentions in particular a piece of cryftal, one part 
whereof, when heated gently, becomes non eledtric ; while the 
other part, with the fame heat, (or even with a much greater one) 
remains perfedlly an eledhic. Vide Vol. L1I. Part i. p. 355* ^ 
have feen the experiments leveral times which Mr. Delaval men- 
tions, and they always fucceeded as he has related them. 
B. Wiifon. 
Memo- 
