332 



Dr. Frankland on some Phenomena 



[March 8, 



rarefaction, the flame became somewhat enlarged, assumed an ellip- 

 soidal shape, and ultimately became almost globular, whilst a large 

 external shell of bluish pink flame gradually came into view as the 

 last portion of yellow light was disappearing from the apex of the 

 flame, which had alone been previously visible. It is scarcely necessary 

 to add, that during these changes in the flame, the light underwent a 

 rapid diminution ; the rate of its decrease, however, was subject to con- 

 siderable irregularities from the heating of the apparatus surrounding 

 the candle, and the consequent guttering and unequal combustion of 

 the latter. For the accurate measurement of the diminution of light, 

 therefore, recourse was had to coal gas, which, although also liable to 

 certain disturbing influences, yet yielded results, during an extensive 

 series of experiments, exhibiting sufficient uniformity to render them 

 worthy of confidence. 



By passing the gas through a " governor," uniformity of pressure 

 in the delivery tubes could be secured; and by other appropriate 

 arrangements a uniform amount of gas, viz. 0*65 cubic feet per hour, 

 was made to burn in each experiment within the atmosphere of varying 

 density. This experimental flame was placed at one extremity of a 

 Bunsen's photometer ; whilst, as a standard for comparison, a similar 

 jet of gas, surrounded by a glass shade, and burning freely in the air 

 with a uniform consumption, was fixed at the opposite end of the photo- 

 meter. In the case of the experimental flame, the products of com- 

 bustion were completely removed, and a steady supply of Tresh air 

 constantly supplied. 



The following table contains a summary of the results of these 

 determinations, the illuminating power given under each pressure being 

 the average of twenty closely accordant observations. In each series 

 the maximum illuminating effect — that is, the light given by the 

 experimental flame when burning under the full atmospheric pressure 

 — is taken at 100. 



FIRST SERIES. 



