100 



SCIENTIFIC RECREATIONS. 



intensity, by advancing or withdrawing one of the two sources of light. 

 The intensities of the two lights will then be inversely proportional to the 

 squares of the measured distances, A B and A c. By a similar careful calcu- 



lation it has been possible to draw up a table of the relative values 

 of various ordinary lights. We have not included here the electric light, 

 which has recently attracted so much attention, because this system of 

 lighting can hardly be said to have yet penetrated the domain of domestic 

 life ; but when we consider electricity, as we hope to do in a future part, we 



