Supplement to Spons' dictionary of engineering Volume 2 ; civil, mechanical, military, and naval

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1880 Excerpt: ...in their lamps the use of the voltaic arc, with what appears to be its necessary attendant irregularity. Higgs's lamp, illustrated in Fig. 1182, is an attempt to avoid as much as possible causes of irregularity, and at the same time to produce a light with small expenditure of power. It utilizes the principles of incandescence, of the arc, and of the extra spark. It consists of an electro-magnet, in face of which is an armature mounted on a spring. The armature carries a block of carbon, iron, or compounded material as a negative electrode, which is not consumed, or is consumed with extreme slowness. The positive electrode is a carbon rod, carried in a tube and falling with a certain friction imposed by a weighted lever, which admits carbon rods of several sizes to be introduced, as may be best suited to the strength of the current. The falling of the carbon can be aided by a weight or spring. The distance of the bottom of the tube from the negative electrode can be adjusted, and limits the length of carbon rod rendered incandescent by the current. When the current passes, through the positive carbon coming into contact with the negative electrode, the armature is attracted, and the voltaic arc and extra spark appear; the current, weakened by this action, fails to keep the armature attracted, and in this manner constant vibration of the negative electrode is established. This vibration is imperceptible to the eye. Its advantage, beyond that of producing the extra spark, which spark itself appears to afford aid in maintaining the voltaic arc, is that the armature has no dead point, and floats, as it were, above the electro-magnet, in a condition to respond promptly to magnetic effects caused by larger increments or decrements of current strength. It is prefe...