The convenience of having at command a small light which will burn all night and give sufficient light to enable the watcher to perform the usual offices of the sickroom has led to numerous inventions having this end in view. One of the oldest was that known as the allnight, which was simply a cake of wax with a slender wick in the center. This was the prototype of the modern mortar, which is merely a very thick dumpy candle with a very slender wick.

In providing a light to burn all night in the sick-room great care should be taken to avoid everything that can injure the air of the apartment. For this reason no volatile combustible, such as kerosene, naphtha, or any similar burning fluid should ever be used: they are sure to give off vapors which make the air offensive and dangerous It is a common practice to use a small kerosene-lamp turned down low. Any person coming out of the fresh air into a room where such a lamp has been burning for some hours, can not fail to notice its injurious effect upon the air; and we can readily imagine what the result must be when the delicate lungs of a sick person are forced to breathe such an atmosphere.

When gas can be had it forms one of the most convenient sources of illumination; but a special burner should be used one which allows very little gas to pass. If we use an ordinary burner and attempt to regulate the flame by the stopcock, much gas will be wasted, and some of it will escape into the room unburned.

One of the best devices is the old "perpetual lamp," as it was called. This consists of a small cup about three quarters of an inch in diameter and made of very thin metal, through the center of which is passed a tube about the sixteenth of an inch in diameter. The tube does not rise in the cup quite to the level of the edge, and by means of a few grains of shot it is easy to sink the cup so that the upper end of the tube will be about the level of the liquid in which the cup is made to float. This liquid is any kind of fixed oil - olive, lard, cottonseed, sperm, etc. It is easy to ignite the oil at the upper end of the tube, when it will continue to burn steadily, and will give a clear and bright but small light for a whole night.

The oil is best held in a glass tumbler, the sides of which allow the light to pass through.

We have often made these night-lamps out of half the shell of an English walnut and a common glass "bugle," such as is used by ladies for trimming some parts of their dress. In the bottom of the shell bore a hole that will just admit the bugle, and fasten the latter in place with a little sealing-wax. Then float the shell in oil, sinking it with fine shot until the oil rises to the upper end of the bugle. As the oil rises considerably by capillary attraction, the top of the bugle will be above the general level of the outside oil by an amount which will depend upon the diameter of the tube. Then hold the flame of a match or well-folded slip of paper over the top of the tube until the oil ignites, when it will continue to burn with a clear steady light until the oil is all gone. Those who prefer to use tallow or solid paraffine can easily keep these substances melted by causing the flame to heat a stout copper wire, which may be bent so as to pass down into the combustible.

Such lights are easily covered, so as to make the room quite dark, by means of an old bandbox or hatbox.