A Cheap Observatory. 241 



matter. This, if the whole thickness of the sensitive coating- 

 has been acted on by the light, intensifies the colours, other- 

 wise it changes the blues to violet, and the black to red. It 

 renders the tint so permanent that, when the iron and copper 

 bath has been used, they are not destroyed by less than ten or 

 twelve hours' exposure to diffused light ; and when the soda 

 bath, not by less than three or four days' exposure to the 

 bright light of summer. The colours, in these processes, 

 make their appearance one after another. Those of natural 

 objects, on account of the white light always mixed with 

 coloured rays, are more or less vitiated ; and when the hues of 

 the spectrum are reproduced, a disagreeable violet shade is 

 found to pervade them all. The binary colours, or those 

 formed by a union of two, are decomposed by heliochromy ; 

 hence the green of the emerald will be reproduced by it ; but 

 the green formed by a mixture of chrome yellow and Prussian 

 blue, will afford only blue. It has been asserted that the 

 colours may be completely fixed by alloxan ; but this requires 

 confirmation. 



Encaustic Photography. A thin glass plate is coated, in the 

 dark, with a mixture consisting of bichromate of potash, honey, 

 white of egg, and water, and dried in a gas stove. It is next 

 placed under a positive, in a copying frame, which produces 

 upon it a weak negative. Pulverized enamel is then rubbed 

 on with a soft brush, until a good positive is produced, which 

 is fixed with alcohol, to which a little acetic or nitric acid has 

 been added ; when the alcohol has evaporated from its surface, 

 it is put horizontally into a dish containing water, and left 

 there until the chromate is dissolved out. The picture in 

 enamel remains, and, having been properly dried, is put into 

 the furnace. 



A CHEAP OBSERVATORY. 



BY FREDERICK BIRD. 



The writer of this article was for several years of the 

 number of those observers who ply their starry occupation for 

 the most part in the open air, and can well sympathize with his 

 brethren under the many difficulties with which their pursuit 

 of knowledge has to be carried on. He commenced his career 

 by casting a metallic speculum, and fabricating a telescope 

 with his own hands. His out- door station Avas at a wooden 

 turn-table, having around it a circular bricked pavement, and 

 many were the delightful hours there spent in hunting up 

 nebula and the double stars. 



