38 LAMPS 



the introduction of gas, very common in shops. The globe A (fy. 1314), which is 

 sometimes made plain and sometimes embossed, as in the cut, screws off, when the 

 oil is poured in at an opening in the lower part, which is afterwards closed by means 

 of a slide attached to the stem B, and the globe, thus replenished, is inverted and 

 screwed into the part c. When the lamp is used, the stem B is raised a little, and the 

 oil is suffered to flow through the intermediate tube into the cistern D, only at the rate 

 at which it is consumed by the burning of the wick. The peculiar form of the glass 

 chimney is admirably calculated to assist in the more complete combustion of the 

 matter drawn up to the wick when impure oil is used, a desideratum originally in part 

 secured by placing over the central tube, and in the midst of the flame, a circular 

 metal plate, by means of which the ascending column of air was turned out of its per- 

 pendicular course, and thrown immediately into that part of the flame where the smoke 

 is formed, and which by this ingenious contrivance is effectually consumed ; this appli- 

 cation, however, is not necessary, nor the form of much moment, when purified sperm- 

 oil is used. These lamps being usually made to move on a pivot at F, attached to the 

 wall or other support, are very convenient in many situations, as being easily advanced 

 over a desk or counter, and afterwards turned aside when not in use. 



The sinumbral lamp having passed out of use need not be described." 



The use of spirit lamps followed, and we have the naphtha and camphine lamps of 

 this order. The accompanying woodcut (fig. 1315) shows the peculiarity of the cam- 

 phine lamp, where .the reservoir of spirit (turpentine deprived of smell) is far below 

 the burner, to which it ascends by capillary attraction, through the tubes of the 

 cotton wick. Lamps to burn naphtha (Belmontine, &c.) are constructed on the same 

 principle, as are all the paraffine and mineral-oil lamps. 



One of the best oil lamps is that known as Carcel's lamp. 



In this lamp the oil is raised through tubes by clockwork, so as continually to 

 overflow at the bottom of the burning wick ; thus keeping it thoroughly soaked, while 

 the excess of the oil drops into the cistern below. Lamps of this description will 

 burn most satisfactorily for many years ; but it can hardly be trusted in the hands 

 of a servant, and when it gets at all deranged, it must be sent to its constructor, in 

 Paris, to be repaired. The light of this lamp, when furnished with an appropriate 

 tall glass chimney, is very brilliant, though not perfectly uniform ; since it fluctuates 

 a little, but always perceptibly to a nice observer, with the alternating action of the 

 pump-work ; becoming dimmer after every successive jet of oil, and brighter just 

 before its return. The flame, moreover, always flickers more or less, owing to the 

 powerful draught, and rectangular reverberatory shoulder of the chimney. The 

 mechanical lamp is, however, remarkable for continuing to burn, not only with un- 

 abated but with increasing splendour for 7 or 8 hours ; the vivacity of the combustion 

 increasing evidently with the increased temperature and fluency of the oil, which, by 

 its ceaseless circulation through the ignited wick, gets eventually pretty warm. In 

 the comparative experiments made upon different lights by the Parisian philosophers, 

 the mechanical lamp is commonly taken as the standard. It is not entitled to this 

 pre-eminence, for it may be made to emit very different quantities of light, according 

 to differences in the nature and supply of the oil, as well as variations in the form 

 and position of the chimney. 



The following experiments by Dr. Ure are well worth preserving : 



The great obstacle to the combustion of lamps lies in the viscidity, and conse- 

 quent sluggish supply, of oil to the wicks ; an obstacle nearly insuperable with 

 lamps of the common construction during the winter months. The relative viscidity 

 or relative fluency of different liquids at the same temperature, and of the same 

 liquid at different temperatures, has not, I believe, been hitherto made the subject 

 of accurate researches. I was, therefore, induced to make the following experiments 

 with this view. 



Into a hemispherical cup of platinum, resting on the ring of a chemical stand, I in- 

 troduced 2,000 water-grain measures of the liquid whose viscidity was to be measured, 

 and ran it off through a glass siphon, ^th of an inch in the bore, having the outer leg 

 3 inches, and the inner leg 3 inches long. The time of efflux became the measure of 

 the viscidity ; and of two liquids, if the specific gravity and consequent pressure upon 

 the siphon were the same, that time would indicate exactly the relative viscidity of 

 the two liquids. Thus, oil of turpentine and sperm-oil have each very nearly the 

 same density ; the former being, as sold in the shops, =0'876, and the latter from 

 0'876 to 0'880, when pure and genuine. Now I found that 2,000 grain-measures of 

 oil of turpentine ran off through the small siphon in 95 seconds, while that quantity 

 of sperm-oil took 2,700 seconds, being in the ratio of 1 to 28J ; so that the fluency of 

 oil of turpentine is 28J- times greater than that of sperm-oil. Pyroxilic spirit, com- 

 monly called naphtha, and alcohol, each of specific gravity 8' 125, were found to run 

 off respectively in 80 and 120 seconds; showing that the former was 50 per cent. 



