A good lamp will fulfil the following conditions: -

1. It will be made of a material not easily broken.

2. Such material, if of metal or other heat-conducting substance, will be insulated from the burner by the use of as long a neck as possible.

3. The actual burner will be continued in the form of a tube containing the wick to within a very short distance from the bottom of the reservoir, thus preventing both the falling of a hot wick into the oil, and the ignition of vapour through contact with it,

4. The reservoir will be made to clip into, and not be loosely borne by, the sconce or cup into which it fits.

5. If the lamp be a high one, its stand or pedestal will be heavily weighted with lead at the bottom.

6. The burner will be screwed on, and not merely cemented or riveted, and such screw will be composed of a good thread for at least four complete turns round the neck of the reservoir.

In the actual use of the lamp, great care should be taken that only a tightly-fitting* wick is used; especially is this the case with round burners, into which only endless wicks, or those perfectly cylindrical in shape, should be fitted in order to avoid the escape of oil previously referred to.

From careful comparison with other illuminants, it would seem that oil takes a high place on account of its comparatively slight contamination of the sur-rounding atmosphere by carbonic acid and other gases. Its heating effects are equally low, though of course in brilliancy it has been far superseded both by electricity and the most modern forms of gas-burners. The approximate cost of using a typical oil-lamp is somewhat similar to that of an Argand gas-burner, as shown by the following table, in which oil, gas, and electricity are compared: -

Table XXXVIII. Comparison Of The Cost Of Illuminants.1

Illuminant

Price.

Burner.

Candle-power.

Amount of illumi nant consumed per hour

Cost per C.P. per hour. in penee.

Oil, .....

per gallon

- 7 1bs 11 ozs.

Lamp

16

2. 08 ozs.

0084

Gas.....

2s. 6d. per 1000 cub. ft.

Ordinary

Bray gas-burner

9.6

6 cub. ft.

•0187

" .......

"

Argand burner

15.8

4.5 cub. ft.

•0085

"

Welsbach incandescent burner

20

4 cub. ft.

•006

" ..........

Electricity,

2d. per unit

Electric incandescent lamp

16

60 watts

0075

" ........

4d. " "

do.

16

do.

•015

1 The following table, translted for this work from the Handbuch der Praktiachen Gewerbehygiene (Berlin, 1896), but thghtly altered in arrangement, goes more fully into the comparison of illuminants, including not only

Bracket, pendent, and table oil-lamps, especially the more expensive kinds, generally have their reservoirs resting in cup-shaped sconces of more or less elaborate workmanship, and fitting therein very loosely to allow of then ready removal, this constitutes a source of considerable danger. While, however, the brackets, pendants, etc, vary greatly in form and constrution, the types of lamps used for them vary very slightly. Hand-lamps are usually safer, as the handles are almost universally attached direct to the reservoirs, thus adding greatly to their stability, and as the reservoirs are usually construeted with much broader bases than other kinds of lamps.

In conclusion may be noticed the two most common methods of suspending and elevating lamps, the apparatus being fitted either direct to the lamps, or (more frequently) to the cup-shaped holders above described. The method most frequently in use is constructed somewhat in the form of a pair of scales, having a long lever suspended by a chain from the ceiling in such a manner that a lamp fixed to one end balances a weight on the other; when the lamp is pulled down the balance-weight goes up, maintaining that position until the lamp is again moved This apparatus has also a circular horizontal movement, allowing the lamp attached to he swung round in a circle of about G feet. The other apparatus consists of a small metal case hung to the ceiling, and containing a thin steel ribbon, which is acted on by a spring adjusted to a tension corre-sponding to the weight of the lamp, by means of a thumbscrew; the lamp, the question of cost but also the important question of the products of combustion. It will be noticed that the round-wicked oil-lamps are, according to the figures in the table, the most economical form of lighting, while the Regenerative and Argand gas-bnrners are both cheaper than electric glow lamps. The Welsbach incandescent gas-burner does not appear to have been tested ; it would undoubtedlt have shown more economical result than any of the other burners mentioned. Of course-, the prodncts of combustion must be considered as well as the cost, and it is in this respect that electricity possesses the greatest merit, and that the ordinary batswing gas-burner shows to the greatest disadvantage. - ED.

Table Xxxviiia General Comparison Of ILI.UMINANTS

Illuminant.

How burnt.

Consumption to obtain a light of 100 candle-powers per hour

Cost per bour In pence.

Products of combustion for equal amount of light.

Water in

Kg

metres.

Heat-

Are lamp, .....

09 - 25 horse power

.6-1. 44

..

..

100

Incandescent lamp.

•46 - .85

1.80

..

..

300

Gas,............

Siemens Regener- tive burner, ..

•35 - .56 cub. metres

72-1.20

..

..

1.500

Argand burner,

•8-2.0

1-74

,86

•46

4,860

Batswing burner. .

2-0 - 8.0

4-52

2.14

1.14

12.150

Petroleum.,.........

Round or "solar" wick........

•28 kilog.

•80

37

•45

3.360

Flat wick,......

•60 .

1-29

.80

.95

7.200

Refined Oil,

Round wick

28 "

•64

•37

.45

3.360

Flat wick,......

.60 .

1.37

.80

•90

7.200

Rape-seed Oil, .....

•50

4.98

.52

•61

4. 200+

Stearine

Candle

.90 "

19.92

1.04

1.30

9.000

being fastened to the end of the ribbon, remains suspended at any distance to which it may be pulled from the ceiling.