It is proposed to give a brief account of the properties of some insulating substances and their application in electrical construction, and at the same time to indicate the appliances and methods requisite for working them. With regard to the specific resistances which will be quoted, the numbers must not be taken to mean too much, partly for the reason already given. It is also in general doubtful whether sufficient care has been taken to distinguish the body from the surface conductivity, and consequently numerical estimates are to be regarded with suspicion. The question of "sampling" also arises, for it must be remembered that a change in composition amounting to, say, 1/10000 per cent may be accompanied by a million-fold change in specific resistance. Sec. 102. Sulphur. This element exists in several allotropic forms, which have very different electric properties. After melting at about 125 deg. C, and annealing at 110 deg. for several hours, the soluble crystalline modification is formed. After keeping for some days--especially if exposed to light--the crystals lose their optical properties, but remain of the same melting-point, and are perfectly soluble in carbon bisulphide. The change is accompanied by a change in colour, or rather in brightness, as the transparency changes. The "specific resistance" of sulphur in this condition is above 1028 C.G.S.E.M. units, or 1013 megohms per cubic centimetre for an electric intensity of say 12,000 volts per centimetre. This is at ordinary temperatures. At 75 deg. C. the specific resistance falls to about 1025 under similar conditions as to voltage. In all cases the conductivity appears to increase with the electric intensity, or at all events with an increase in voltage, the thickness of the layer of sulphur remaining the same. The specific inductive capacity is 3.162 at ordinary temperatures, and increases very slightly with rise of temperature. [Footnote: March 1897.--It is now the opinion of the writer that though the specific inductive capacity of a given sample of a solid element is perfectly definite, yet it is very difficult to obtain two samples having exactly the same value for this constant, even in the case of a material so well defined as sulphur.]