Mr B. Martin’s Experiments on Island Crystal. £55 
a lid that slides on and off. This box is divided into six cells 7 
in these I put prisms arid parallelopipeds of glass, and Iceland 
crystal, with proper holes on each side for light to pass through 
them. Then a box-holder being made of springy thin brass, 
with a motion every way, is screwed on to the apparatus of a so- 
lar microscope, in the room or place of Wilson’s microscope ; 
and the long box being put into the holder, and the looking- 
glass adjusted to reflect the sun-beams horizontally, they will 
pass through the glass or crystal that is placed in them succes- 
sively ; and all the variety of refractions, and their coloured 
images, will appear, under all the advantageous circumstances, 
by the motion of the box, so as to produce the most delectable 
entertainment to a curious mind. 
44 And here I cannot help making a few reflections on the 
unequal, or rather iniquitous estimation of things in general. 
What a value do we often set upon that which has no real worth 
at all P Wherein does the preciousness of most precious stones 
consist ? And who can account for the princely esteem of an oys- 
ter shell pearl ? 
44 Something, indeed, may be alleged in favour of the most 
extravagant valuation of a diamond ; but what is it ? why, only 
this, that it exceeds all other bodies in transparency, brilliancy , 
and hardness ; yet all this amounts to nothing more than a su- 
periority of the common qualities of natural bodies : it has no 
new, singular, or peculiar property of its own : It may make a 
man more splendid, but cannot make him wiser, at least by 
wearing it in his hat, or a diadem. On the other hand, how 
notoriously are things of the greatest value overlooked, neglect- 
ed, or disesteemed ! Amongst a hundred other curious subjects, 
let Iceland crystal prove this truth,— a body of a most singular 
nature and endowment, yet little known or inquired after,— -a 
subject without a compeer in nature ; for though amber *, borax, 
pebble, &c. are found to have a double refraction, it is in no sen- 
sible or significant degree. — No substance but Island crystal has 
a multuple and multifarious refraction of light, even to an un- 
known degree. — No crystal but this, with parallel sides , pro- 
duces any colorific refraction of the solar rays. — No pellucid 
* By Amber the author must mean Mdlite , as the separation of the rays can* 
not be seen in Amber.— Ed. 
