34 REPORT—1849. 
ral groups to be embraced in the picture, and the distance of that plane properly 
proportioned to the breadth of the picture. 
The President exhibited a Universal Sun-dial, made by Mr. Sharp of Dublin. It 
consists of a cylinder, set to the day of the month, and then elevated to the lati- 
tude. A thin plate of metal in the direction of its axis is then turned by a milled 
head below it till the shadow is a minimum, when a dial on the top shows the 
hours by one hand and the minutes by another. It appears that the time can be 
obtained by this to the precision of about three seconds. 
CHEMISTRY. 
Inquiries on some Modifications in the Colouring of Glass by Metallic Oxides. 
By G. Bonrtemps. 
In this communication some important practical points connected with the coloured 
ornamentation of glass and porcelain were brought forward. In the first place, it was 
shown that all the colours of the prismatic spectrum might be given to glass by the 
use of the oxide of iron in varying proportions and by the agency of different degrees 
of heat; the conclusion of the author being, that all the colours are produced in 
their natural disposition in proportion as you increase the temperature. Similar 
- phenomena were observed with the oxide of manganese. Manganese is employed 
to give a pink or purple tint to glass, and also to neutralize the slight green given by 
iron and carbon to glass in its manufacture. If the glass coloured by manganese re- 
mains too long in the melting-pot or the annealing-kiln, the purple tint turns first to 
a light drownish-red, then to yellow, and afterwards to green. White glass in which 
a small proportion of manganese has been used is liable to become light yellow by ex- 
posure to Juminous power. This oxide is also in certain window-glass disposed to 
turn pink or purple under the action of the sun’s rays. M.Bentemps has found that 
similar changes take place in the annealing-oven. He has determined, by experiments 
made by him on polyzonal lenses for M. Fresnel, that light is the agent producing ~ 
the change mentioned ; and the author expresses a doubt whether any change in the 
oxidation of the metal will explain the photogenic effect. A series of chromatic 
changes of a similar character were observed with the oxides of copper; the colours 
being in like manner regulated by the heat to. which the glass was exposed. It was 
found that silver, although with less intensity, exhibited the same phenomena; and 
gold, although usually employed for the purpose of imparting varieties of red, was 
found by varying degrees of heating at a high temperature and recasting several times, 
to give a great many tints, varying from blue to pink, red, opake yellow and green. 
Charcoal in excess in a mixture of silica-alkaline glass gives a yellow colour, which 
is not so bright as the yellow from silver; and this yellow colour may be turned to 
a dark red by a second fire. The author is disposed to refer these chromatic changes 
to some modifications of the composing particles rather than to any chemical changes 
in the materials employed. 
On an Improvement in the Preparation of Photographic Paper, for the purposes 
of Automatic Registration ; in which a long-continued action is necessary. 
By C. Brooks, F.RS. 
The preparation of the paper described previously, may be thus briefly stated. 
The paper is washed over by a brush with a solution of 12 grs. of bromide of 
potassium, 8 grs. of iodide of potassium, and 4 grs. of isinglass in one fluid ounce of di- 
stilled water, and dried quickly. When about to be used, it is washed over bya brush 
with a solution of 50 grs. of nitrate of silver to 1 fluid ounce of water, and placed on 
the cylinder of the registering apparatus, on which it remains in action for twenty- 
four hours. When removed, the impression is developed by brushing over a warm 

