82. The ^hQamral Hifiory 
ealieft of any of them, in a planum to the more deprelTed Rbom- 
hoideal fides ; which way it may be cut into very thin plates by 
Aldrovandu6 called Scaias^ for which reafon 'tis called alfo A- 
lumen ScaioU ; not that it has thetaft of or any thing like 
it. It breaks alfo another way into fmall threds^ of which it 
feenis chiefly to be compofed, much after the manner of Amian- 
tws or 7alc^ but its parts not fo pliant as either of them : thefe 
thrcds lie for the moft part, clofe and paralel to the longer fides 
of the great i^/'owZ'o/Wi, as they are defcrib'd in 7df^. 2. though 
I have feen them fomtimes alfo parallel to the (liorter ; 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 like wife be feen 
in Fig. I, a. In thefe lines its parrs are alfo eafily feparated, but 
breaking fliort 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 reprcfent the 
Rain-bow^ whereof I have fome with the colours as vivid, as I 
ever faw any in a glafs Prifm, Of thefe Aldrovandws had one out 
of Cyprus ^ of which he has gi ven us a C ut in his Muf<xum ' ; but it 
being in Mans power co 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 depre{redfides,and fcarce 
any angles^ but what are fo obtufe that they deferve not the name, 
in the whole almoft of an Oval form, as reprefented 7*^^.2. Fig. i-^. 
This fort of Selenites, befidesthe lliape, is alfo fo different from 
the former in texture,that it flits not like that into plates or fcales, 
parallel to the moft deprelTed fides, but quite contrary parallel 
to the thicknefs only ; which I take to be a charaSkr abundantly 
fufiicient, to make it of a dift'erent /pedes 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 'rmkes it the dew of Heaven, congeled, as 
he fays, by the light of the ^^oon^ and therefore calls it by the 
n2.meo^ Jphrofelinum^ but reftrains the performance of the feat 
q Mu/leum Metallkum,lib. ^.cap. 33. f Li&.^.cap. 33' * Lih de Simp- Med- ad Fateiit, 
to 
