144 Notice respecting the House of Copernicus. 
In all the crystals which I have examined ^ including Apophyl- 
lites from Fassa, Utoe, Faroe, and Iceland, the doubly refracting 
force as exhibited by a distinct separation of the images, was 
Positive or Attractive, whether the ray was red, blue, or yellow. 
I therefore consider the property discovered by Mr Herschel 
as belonging only to some particular crystals, or parts of crys- 
tals, in which one of the three positive axes has had its intensity 
reduced. Specimens will, I have no doubt, yet be found, in 
which the Apophyllite exerts a Negative action on all the rays 
of the spectrum ; for I have shewn in the paper already quoted, 
• that the intensity of the principal axis varies in the same crys- 
tal according to a regular law, and that all its variations are 
symmetrical, in relation to the centre or the summits of a com- 
plete crystal. Hence, it is extremely probable, that the points 
or nodes at which the negative passes into the positive structure, 
may be found in the same crystal, and near the points «, b in 
Fig. 13. of my paper on Apophyllite ; for in several crystals the 
transition at these points appeared to be very sudden. 
Art. XXII. — Notice respecting the House, ^c. of Copernicus > 
In a Letter from George Harvey, Esq. Member of the 
Astronomical Society. 
Dear Sir, 
In a former number of your valuable Journal, you introdu- 
ced a very interesting fac simile of one of the letters of the 
celebrated Copernicus. I am a lover of such fragments, be- 
cause they awaken associations of a pleasing kind ; and in 
moments of difficulty and depression, bring accessions to human 
happiness, more consolatory than all the pleasures which power 
can command. 
By the kindness of a scientific friend, I have been favoured 
with the inclosed sketch of the house in which this illustrious 
astronomer resided * ; and also of the chair in which he was 
accustomed to sit. The pyramidal figure near the house, is the 
well which supplied him with water. They have afforded me 
See Plate II. Figs. 5. and 6. 
