Insulation, Our Indian Telegraphs

[From the Telegraphic Journal.]

Insulation. — Our Indian Telegraphs.

To the Editor of the Telegraphic Journal.

SIR — In the extract given in your number of May 15th, from THE TELEGRAPHER of April 5th, 1873, headed, "On Economical Line Construction," Mr. Brooks, in the second column, enters into a consideration of the gain in money and loss in current produced by using for a land line a thin wire instead of a thick one. He states that when the absolute conduction resistance is increased 22 per cent. the loss so produced can be compensated for by increasing the battery power 22 per cent.

Now this is far from being the case in a long or badly insulated line, since an increase on the conduction resistance not only diminishes the current leaving the sending station, but in addition diminishes the proportion of the sent current arriving at the receiving station, so that an increase in the conduction resistance produces a double diminution in the received or effective current. This will perhaps be more clearly seen from the following consideration:

Let the absolute conduction resistance of a line be (2 R), the absolute insulation resistance (B), the resistance of the relay at the distant end of the line (D), and the electro-motive force of the sending battery (E), then, if the line be uniformly insulated, and if we neglect the resistance of the battery itself-which is usually small compared with the other resistance in circuit-we have the received current equal to

BE

A(2B+D)+A2 +BD

Now, if (A) be not small in comparison with (B), which will be the case in a long or badly insulated line, increasing (A) by 22 per cent. will diminish the above fraction by far more than 22 per cent.; consequently it will require that be should be increased by far more than 22 per cent. to keep the received current constant. The use, therefore, of thick wire for long land lines, possesses far greater advantages than Mr. Brooks has attributed to it.

This gentleman then proceeds to quote an article from "one of the leading scientific journals," in which it is stated that "there is no place in the world where there is such a lack of scientific knowledge in connection with the telegraph service, except America, as in the British East Indies." Probably this gentleman is not aware that Mr. Latimer Clark (who, when on a visit to India, examined the telegraphs of that, country) stated recently, while occupying the President's chair at the Society of Telegraph Engineers, that "although some six years ago the Indian Government Telegraph was, perhaps, one of the most unscientific in the world, that now it had attained the foremost place amongst telegraphic administrations in the application of scientific laws to practical questions."

Mr. Brooks seems also unacquainted with the "Instructions for Testing Overland Telegraph Lines," compiled by Mr. Schwendler, of the Indian Government Telegraph, and issued to the officers of that department June 18, 1869, since Mr. Brooks' "Method of Determining the Actual Resistance of Old Telegraph Line Wires," which he gives as new in THE TELEGRAPHER. April 5, 1873, may be found not only in extenso in the "Instructions" referred to above, but, in addition, with what is most essential in practice (but what is not given by Mr. Brooks), methods for determining the exact position of the "single leak," and for freeing all the results from the effects of natural line currents.

If Mr. Brooks wishes to see what scientific work is being done, and has been done by the Indian Government Telegraph, I would refer him to "The Instructions for Testing Telegraph Lines, and the Technical Arrangements in Offices," the first part of which was published in the beginning of 1872 by that department, the second and third parts being probably also now ready. These "Instructions." in three parts, are founded on those issued in 1869, but are much more elaborate and complete.

I am, &c.,

W. E. AYRTON,

Prof. Nat. Phil., The Imperial College of Engineering, Tokei, and Hon. Sec. for Japan of the

Society of Telegraph Engineers.

[Mr. Ayrton is in error in attributing to Mr. Brooks the article entitled "Method of Determining the Actual Resistance of Old Telegraph Line Wires." Mr. Brooks' article "On Economical Line Construction" appeared in THE TELEGRAPHER of April 5th, 1873, while the other article referred to was published one week later (April 12th), under the signature of "J. H." Mr. Brooks knew nothing of it in any way. The greater part of the article appears to be a literal translation of Mr. J. Hager's article on the same subject in the Annales Telegraphiques, July-August 1865, though we are quite positive that Mr. Hagers was not the J. H. who sent it to us for publication.   Any one who knows anything of Mr. Brooks will agree with us that he is about the last person in the world who would be likely to appropriate other people's ideas and pass them off as his own. As far as regards the criticism on his article, he will probably speak for himself. - ED. TELEGRAPHER.]