268 SCIENCE IX SHORT CHAPTERS. 



nry, the big-flame candle made of Knssian tallow, with a wick of 

 Transatlantic cotton. Presently this luxurious innovation was 

 superseded by the " mould candle ;" the dip was consigned to the 

 kitchen, and the bloated aristocrats of the period indulged in a pair 

 of candlesticks, alarming their grandmothers by the extravagance of 

 burning two candles on one table. Presently the mould candle was 

 snuffed out by the composite ; then came the translucent pearly par- 

 affine candle, gaslight, solar lamps, moderator lamps, and parafnne 

 lamps. Even these, with their brilliant white flame from a single 

 wick, are now insufficient, and we have duplex and even triplex 

 wicks to satisfy our demand for glaring mockeries of the departed 

 sun. 



Some are still living who remember the oil lamps in Cheapside and 

 Piccadilly, and the excitement caused by the brilliancy of the new 

 gas lamps ; but now we are dissatisfied with these, and demand 

 electric lights for common thoroughfares, or some extravagant com- 

 bination of concentric or multiplex gas-jets to rival it. 



The latest novelty is a device to render darkness visible by captur- 

 ing the sunbeams during the day, holding them as prisoners until 

 after sunset, and then setting them free in the night. The principle 

 is not a new discovery ; the novelty lies in the application and some 

 improvements of detail. In the "Boy's Own Book," or "Endless 

 Amusement," of thirty or forty years ago, are descriptions of " Can- 

 tm's phosphorus," or " solar phosphori," and recipes for making 

 t'lem. Burned oyster-shells or oyster-shells burned with sulphur, 

 was one of these. 



Various other methods of effecting combination between lime or 

 baryta with sulphur are described in old books, the result being the 

 formation of more or less of what modern chemists call calcium sul- 

 phide and barium sulphide (or otherwise sulphide of calcium or sul- 

 phide of barium). These compounds, when exposed to the sun, are 

 mysteriously acted upon by the solar rays, and put into such a con- 

 di:ion that their atoms or molecules, or whatever else constitutes 

 their substance, are set in motion in that sort of motion which com- 

 municates to the surrounding medium the wavy tremor which 

 agitates our optic nerve and produces the sensation of light. 



Until lately, this property has served no other purpose than puz- 

 zling philosophers, and amusing that class of boys who burn their 

 fingers, spoil their clothes, and make holes in their mothers' table- 

 covers, with sulphuric acid, nitric acid, and other noxious chemicals. 

 The first idea of turning it to practical account was that of making a 

 sort of enamel of one or the other of these sulphides, and using it as 

 a coating for clock-faces. A surface thus coated and exposed to the 

 light during the day becomes faintly luminous at night. 



Anybody desirous of seeing the sort of light which it emits may 

 do so very easily by purchasing an unwashed smelt from the fish- 

 monger, and allowing it to dry with its natural slime upon it, then 

 loeking at it in the dark. A sole or almost any other fish will answer 

 the purpose, but I name the smelt from having found it the most 

 reliable in the course of my own experiments. It emits a dull, 

 ghostly light, with very little penetrating power, which shows the 

 shape of the fish, but casts no perceptible light on objects around. 



Thus the phosphorescent parish-clock face, with non-phosphores- 

 cent figures and hands, would look like a pale ghost of the rncon with 



