$z The Statural Hijlory 



eafieft of any of them, in ^planum to the more depreffed Rbom- 

 boideal fides ; which way it may be cut into very thin plates by 

 Aldrovandu* 1 *, called Scaiat, for which reafon 'tis called alfo A- 

 lumen ScaioU ; not that it has thetaft of Alum, or any thing like 

 it. It breaks alfo another way into fmall threds, of which it 

 feems chiefly to be compofed, much after the manner of Amian- 

 tus or Talc, but its parts not fo pliant as either of them : thefe 

 threds lie for the moft part, clofe and paralel to the longer fides 

 of the great Rhomboids, as they are defcrib'd in Tab. 2. though 

 I have feenthem fomtimes alfo parallel to the fhorter ; but they 

 feem not to be continued the whole bredth of the Rhomboid, but 

 divided by other parallel lines of a greater diftance, that fom- 

 times are fubtended to the acute angles of the Rhomboid, but moft 

 commonly run in a more oblique pofture,as may likcwife be feen 

 in Fig. 1. a. In thefe lines its parts are alfo eafily feparated, but 

 breaking (bort off, and nothing fo flexible as they are when bro- 

 ken as the threds run. According to fome peculiar pofitions 

 of thefe parts, there are fome of them that really reprefent the 

 Rain-bow, whereof I have fome with the colours as vivid, as I 

 ever faw any in a glafs Prifm. Of thefe Aldrovandm had one out 

 of Cypm, of which he has given us a Cut in his Mufieum' ; but it 

 being in Mans power to make thefe Rain-hows as he pleafes, I 

 think even thofe we find thus, to belong of the two rather to ca- 

 fualty than nature, and therefore pafs them by. 



8. There is, 'tis true, a fort of them of a different figure, not 

 fo eafily to be met with, with only two depreffed fides,and fcarce 

 any angles, but what are fo obtufe that they deferve not the name, 

 in the wholealmoftofan Oval form, as reprefented 7d. 2. Fig. i. 

 This fort of Selenites, befides the fhape, is alfo fo different from 

 the former in texture,that it flits not like that into plates or fcales, 

 parallel to the moft depreffed fides, but quite contrary parallel 

 to the thicknefs only ; which I take to be a character abundantly 

 fufficient, to make it of a different fiecies from the other, though 

 in the reft of their texture they be much the fame. 



9. About the origin of this matter, Authors differ much ; a- 

 mongftwhom Galen * makes it the dew of Heaven, congeled, as 

 he fays, by the light of the Moon, and therefore calls it by the 

 name of Jphrofelinum, but reftrains the performance of the feat 



q Mufeum MetaUicumJib. ^ cap. 33. r Lit. ^. cap. 33- Lib deSimp. Med- ad Paters. 



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