4. In the generality of cases coloring matters, such as indigo, Indian yellow, madder-lake, and the like, do not separately exist in the substance of vegetables, but the pigments are disengaged through fermentation or oxygenation. Again, alizarin itself is reddish yellow, but alkaline solutions strike it a rich violet, just as we find them act towards the substance which Mr. Sorby calls Aphidilutein.

5. Mr. Sorby's four stages of the changes effected by the oxidation of Aphideine produce four different substances.

The different colors produced by the use of different chemicals must be compared in Mr. Buckton's paper. But there can be no doubt that here colors are produced chemically out of protein-bodies,

a fact somewhat homologous to the before-quoted artificial production of indigo.

The influence of temperature on the colors of the imago of Lepidoptera was first shown by Mr. Dorfmeister. He proved that a higher temperature changes the reddish-yellow of the hind-wings of Bombyx caja to minium, a lower temperature to ochreous yellow. The changing of spring-races of butterflies into autumn-races by putting the chrysalis on ice, the well-known experiments made by Mr. W. H. Edwards and Prof. Weismann and others, show unquestionably the influence of temperature on colors. Probably here the change is the effect of a surplus of nitrogen. The water absorbs a small quantity of air, but in such a manner that this air contains less than two parts (1.87) of nitrogen to one part of oxygen, instead of four parts of nitrogen. Therefore an excess of nitrogen in the surrounding air must be the consequence, as is the case in the iced chambers of fruit-houses, where the oxygen is purposely rarefied in relative quantity. By this nitrogen, together with the nitrogen contained in the chrysalis, life and development are retarded to a minimum ; but the chemical action which produces colors will work nevertheless to a certain extent. Therefore a change in the colors of the imago is the necessary consequence, and this change affects probably the pattern, which is, as stated before, produced largely by oxygen, which is here rarefied.

Goethe has characterized the yellow and related colors as acid ones, the blue and related as alkaline colors. He states that vegetable yellow colors can be changed by alkali into red, or even into blue red.

For plants the predominant color is green, for insects brown; both of which are called indifferent colors.

FINAL CONCLUSIONS.

If color and pattern are produced in a purely mechanical manner, as Prof. Weismann contends, it ought to be possible to explain and to prove this mechanical manner, if we will go beyond the simple belief that it is so.

The foregoing review contains all that is known about these questions:

1. That some colors of insects can be changed or obliterated by acids.

2. That two natural colors, madder-lake and indigo, can be produced artificially by the influence of acid on fat bodies.

3. As protein bodies in insects are changed into fat bodies, and may be changed by acids contained in insects into fat acids, the formation of colors in the same manner seems probable.*

4. That colors can be changed by different temperature.

5. That the pattern is originated probably by a combination of oxygen with the integuments.

6. That mimicry of the hypodermal colors may be effected by a kind of photographic process.

In comparing these still insufficient data with the statement - that color and pattern are produced in a purely mechanical manner, and are the consequences of natural selection, of adaptation, and of inheritance, we must, if we wish to go beyond belief, directly exclude inheritance, as after the statement of Professor Weismann himself† it is entirely unknown how inheritance works; even the question itself is still entirely untouched. We must further exclude natural selection and adaptation, as both are (according to Professor C. Semper ‡) only able to begin to work after pigment is produced and after a change of the pattern has begun.

What is then left to justify our accepting a purely mechanical manner but the simple belief that it is so?

I am convinced that color and pattern are produced by physiological processes in the interior of the bodies of insects.

* Dr. R. Sachse: Die Chemie und Physik der Farbestoffe, Kohlenhydrate u. Proteinsubstanzen, p. 288 sqq. Leipzig, 1877.

† Dr. A. Weismann: Die Dauer des Lebens, 1882; and Studien, vol. ii. p. 296.

Professor C. Semper: Die natürlichen Existenz-bedingungen der Thiere, 1880. Vol. i., p. 265; vol. ii. p. 232.

XV.

ON TELEPHONING OVER LONG DISTANCES OR THROUGH CABLES.

BY N. D. C. HODGES.

Presented May 10, 1882.

THE first point I wish to bring up is, that within any conductor connected with the earth the only electrical forces against which work has to be done during the movement of electrified bodies are those due to the mutual actions between the charges in these bodies, and not to the charges which may exist outside the conducting surface. So that in causing a movement of electricity from A to B, the work is the same when A and B are inside a conducting surface as when they are outside; and to cause a current along any course from A to B, the same amount of energy will be required as if the system A B were in open space.

Hence in the case of a double-wire cable of no great length compared with its section, so that the resistance of the wire should not be sufficient to cause it to act like a succession of short pieces, the source of the electromotive force being contained in a conducting surface continuous with the outside of the cable, a current could be produced as easily as in an air-line.

In the next place, in the case of a cable we have a condenser to deal with, the circuit wire being the inner, and the water outside the outer surface. In order to cause a current to flow through a conductor situated in this way, a quantity of electricity must be supplied sufficient to raise the potential along the conductor to such a degree that the required current may flow.

To raise the charge of a conductor, the work to be done is expressed by V, where is the final charge of the conductor and Vits poten

8

tial; or, in terms of the capacity and potential, q V2.

For a single wire surrounded by a homogeneous non-conductor to an indefinite distance, the electric capacity is

length of the wire and a its radius.

where is the

log

For a wire surrounded by a homogeneous dielectric to a limited where K is the specific inductive

distance, the capacity is

ΚΙ

log 21

capacity of the dielectric, and a, and a, the outer and inner radii of the dielectric.

As the energy required to charge a condenser is

and as no work is done in moving the one conducting surface within the other, the same expression for the work done in charging a cable will hold when the wire is not concentric with the outside as when it is, as was supposed in the above.

Hence the work required to charge a unit length of cable, even when the wires are not in the centre, will be equal to

On account of this static capacity of a cable, there is a retardation in the transmission of signals from the greater amount of energy which must be supplied from the electrical source before the potential along the wire will be raised sufficiently to cause the required current; just as, in the case of heat, the specific heat of a bar determines how much heat must be given to one end of the bar before heat will flow along the bar at any given rate.

With a single wire cable let V be the potential at any point of the wire. Let be the total quantity of electricity which has passed through a section of the cable at that point since the beginning of the current. Then the quantity which at the time t exists between sections at x and x + dx is

With a double-wire cable when used to form a metallic circuit, the two wires being connected to the two poles of the battery or transmitter, or whatever the electric source may be, the quantity of electricity flowing across any section of the cable on one of the wires will be equal and of opposite sign to that on the other.

Hence the total quantity flowing across any section of the cable will be zero, and dQ will be zero. So that the potential to which the condenser, consisting of the two wires and the outside surface of the cable, will be raised will be zero, and the energy required from the battery no greater on account of the nearness of the water, the second conducting surface of the condenser.

There is one thing to be considered, that the wires, being covered with some insulating material which cannot be made perfectly homogeneous, they, with the broken nature of the dielectric about them, will each form a condenser to some extent.

It would therefore appear that, as far as the retardation is due to the static capacity of a cable, it can be greatly reduced by using a double wire cable with homogeneous insulating material.

In support of this view there are the experiments made by Wheatstone, and described in the Proceedings of the Royal Society for 1854-55. Wheatstone made experiments on a cable of six wires intended for use in the Mediterranean. The length of the cable was one hundred and ten miles. On connecting one of the wires with one pole of his battery, the other pole being to ground, he found that quite a time was required before the flow into the cable fell to the rate due to leakage. On connecting one pole of the battery with one wire and the other with another, the charge which the cable wires would take was reached instantly.

On long land lines the static capacity of the line is due, outside of the capacity of the wire, to the neighborhood of the earth. This has been found to affect the articulation in telephoning on the line from Boston to Baltimore, five hundred miles in length. By the use of a complete metallic circuit the articulation was greatly improved.

SALEM, MASS., U. S. A.,

May 9th, 1882.