436 MR. HIGGINBOTTOM ON THE INFLUENCE OF PHYSICAL AGENTS. 
At the first I was led to think the absence of light was even favourable to deve- 
lopment, but I afterwards found that the difference depended on a slight increase of 
temperature owing to the vessel being covered. This fact is rendered obvious by the 
Plate, in which the temperature and absence of light are fully illustrated. 
Nottingham, 
February 5, 1850. 
P.S. I made these experiments in 1848 ; they were repeated in the year 1849 with 
similar results. 
