86 The Rev. Dr. Callan's Eocperiments on the 



up for eighteen hours ; for the light would last only five seconds 

 in each minute, and couseqtiently only five minutes in each hour, 

 or an hour and a half in eighteen hours. Therefore, since the 

 three gas bags, filled with the mixed gases, would maintain a 

 constant light for an hour and a half, they should keep up the 

 intermittent light for eighteen hours. I believe such an inter- 

 mittent would answer very well for lighthouses. In the light- 

 house on the eastern pier at Kingstown, the light is a revolving 

 one, which completes a revolution in about a minute. The bril- 

 liant white light, the only one which can be seen at a distance, 

 shines out only for about five seconds in each minute. Hence 

 I infer that an intermittent lime light which lasts for five seconds 

 in each minute would be sufficient for lighthouse purposes. It 

 is necessary to observe, that, when gases are gradually cut ofi" 

 from the jet, the gases in the upper part of the voltameter, or 

 vessel to which the jet is attached, will explode if a Hemming's 

 jet be not used ; and this explosion, though perfectly free from 

 danger, will be attended with inconvenience, for a vacuum will 

 be produced in the upper part of the voltameter or vessel, 

 and no gases can pass to the jet till this vacuum is filled. 

 Hence, in producing an intermittent lime light, a Hemming's 

 jet should be employed. Since the discovery of the cast-iron 

 battery, several persons have obtained patents for apparatixses 

 for the coke light, or, as it is now called, the electric light. If 

 they arranged their apparatus so as to produce an intermittent 

 coke-light similar to the intermittent lime light I have described, 

 they would confer a great benefit on society. When the coke 

 light is constant, the battery is soon exhausted, the coke points 

 are consumed, and must be frequently renewet^ ; but were the 

 light intermittent, a single charge of the battery might last for 

 an entire night, and it would be sufficient to renew the coke 

 points two or three times in the course of the night. And if an 

 intermittent coke light were used in lighthouses only on very 

 dark and foggy nights and in snow-storms, the expense could not 

 be considerable. I think the coke light is more intense than 

 the lime light, and also somewhat less expensive. To produce 

 a coke light sufficient for all illuminating purposes, forty cast- 

 iron cells, each containing a zinc plate 2 inches by 4, will suffice. 

 To obtain a lime light of equal illuminating power, a battery 

 containing at least twice as large a surface of zinc will be required. 

 A battery with a given charge will scarcely work twice as long 

 in decomposing water as in igniting a pair of coke points. There- 

 fore, on the whole, I think the lime light is more expensive, but 

 much more easily managed than the coke light. The former 

 requires a battery of only four large plates ; the latter depends 

 on the intensity of the current, and requires a battery of at least 

 thirty-five or forty cells. The coke points will require to be 



