84 Mr Dunlop's observations on the Comet of 1825. 



the advantage of containing no element in the least degree pre- 

 judicial to health. The others have been quoted principally to 

 show the true nature of the action which takes place in ginger- 

 bread-dough, in the present tardy process, as well as in the 

 other methods. There is yet another process of gasification, 

 however, which should be mentioned, as it is occasionally re- 

 sorted to in the manufacture of this kind of bread, as well as in 

 that of many others, and with the same complete success. This 

 is by using the sesqui-carbonate of ammonia, whose efficacy and 

 the nature of whose action in expanding all kinds of dough in 

 the process of baking, have already come under our notice. If 

 this salt be employed in the proportion of half an ounce to the 

 pound of flour, the dough containing it, however recent when 

 baked, will always form itself into a good light bread ; and it is 

 on this account a very common practice with the baker to add a 

 certain quantity of it to his ordinary gingerbread-dough, when he 

 is under the necessity of employing it in its recent state, before 

 it has been sufficiently matured by keeping. The bread so 

 formed is found to possess an extremely agreeable flavour, and 

 it is also marked by the peculiarity of having the upper surface 

 unusually dark and glossy. In this bread, also, as in others 

 similarly aerified, there remains always a certain trace of am- 

 monia, which would be plainly perceptible, but for the confec- 

 tions which disguise it." 



Art. X. — Observations on the Comet of 1825, and on the 

 Changes which take place in the figure of the tail, tending 

 to establish the existence of a rotation round its axis. By 

 Mr James Dunlop, Paramatta. Communicated by Sir Tho- 

 mas Makdougall Brisbane, K. C. B. F. It. S. London 

 and Edinburgh. 



On the 21 st July 1825, I discovered a body, nearly in the pa- 

 rallel of 44 Taurus, which I strongly suspect to be a very small 

 comet ; the nebulosity is exceedingly faint. I can perceive ra- 

 ther a condensation near the south following extremity ; the ne- 

 bulosity is perhaps two minutes in length, and nearly one mi- 

 nute broad. 



