142 Mr Tait on a Portable Diorama. 
forded the different tints. Thus, when it is diffused in a so- 
lution of triple prussiate of potassa, the addition of sulphate 
of iron produces a fine blue; when diffused in a solution of 
chromate of potassa, sugar of lead affords an excellent yellow. 
It is more difficult to procure a fine green from copper. Ihave 
not yet succeeded in procuring by precipitation so beautiful 
a green as that prepared in Glen Sannox. A fine green was 
obtained by precipitating Scheele’s green, or the sulphate of 
baryta diffused in a solution of ammoniaco-sulphate of copper 
by means of arsenic. 
The remarkable fact is, that when thus precipitated, the 
colouring matter is less easily separated by acids than from 
mere mixtures of the materials ; as if there was some athinity 
between the metallic colours and the sulphate of baryta. 
Description of a Portable Diorama, constructed by Grorce 
Tarr, Esq. Advocate. Communicated by the Royal Scot- 
tish Society of Arts. 
Tue diorama, the ingenious invention of the celebrated 
French artist Daguerre, is a painting fitted up so as to re- 
ceive light both in front and behind, by the full or partial 
admission, or the total exclusion, of either of which lights a 
great variety of effects may be produced. No light is admitted 
to the eye except that which proceeds from the painting. 
The diorama is usually executed on an extensive surface 
of canvass, and placed in a large building fitted up for the 
purpose. 
It occurred to me that it might be made upon a much 
smaller scale ; and, accordingly (before the publication of Da- 
guerre’s description), I constructed for the reception of sketches 
in water-colours, which I painted for the purpose, a small box 
having, for the admission of light before and behind, openings 
capable of being closed by moveable shades, and having also 
a small opening in front through which the sketches might be 
viewed. Upon trying a variety of sketches in this apparatus, 
I have found that many pleasing and striking effects may be 
produced ; for example, passing gleams of sunshine; day 
melting into moonlight ; day fading into darkness, followed 
by morning gradually disclosing the landscape, having its for- 
mer verdure shrouded in snow. 
