[Trade Journal]
Publication: The Telegrapher
New York, NY, United States
vol. 5, no. 34, p. 1, col. 1-3
AN EMINENT ELECTRICIAN.
THE Journal of the Telegraph, in its issue of April 1st, editorially compliments very highly Mr. Moses G. Farmer, of Boston, Mass., as a practical telegrapher and electrician.
In speaking of his invention of the American compound wire, it says of him: "Here, however, is an article, the fruit of the brain of one of the best known practical telegraph and electric workers, of a man thoroughly honest and in earnest, who has given these last twenty-five years and more to the patient, careful, thorough examination of not only electric science, but of the means by which that science can subserve in the best way and widest extent the public necessities. We need not recapitulate all heh as accomplished, for every intelligent operator, and everyone who has followed the literature of the telegraphic art in America, knows the name of Moses G. Farmer, of Boston. We regard him as one of those to whom it is a richer compensation to add to the present knowledge of the capacities of the telegraphic art than any mere gain from the sale of his inventions. For this reason we are led to estimate highly the products of his industry."
We have for many years enjoyed the privilege of an acquaintance with Mr. Farmer, and can fully and unequivocally endorsee very word of the above. His attainments as a telegrapher and electrician are fully equal, if not superior, to those of any person in this country or abroad. Like the late Prof. Faraday, he devotes himself to science for the love of science, and for the discovery and development of principles which shall prove useful and beneficial to mankind, and not for purposes of gain and emoluments.
His discoveries and inventions in electrical science and art have been numerous and valuable, and in the hands of almost any man whose idea was primarily that of gain, would have brought the inventor wealth to any desired amount.
Mr. Farmer has recently devoted much time and attention to testing and comparing different varieties of insulators. As every telegrapher and electrician knows, upon the more or less perfect insulation of the wires mainly depends the good or bad working of the instruments, and it is therefore of the utmost importance that the insulator should be generally adopted which will give us, as nearly as possible, perfect insulation under all atmospheric conditions.
It will be seen, from the following statement of Mr. Farmer, that Brooks' Improved Paraffine Insulators sustained the excellent reputation which the results of actual use has given them, under Mr. Farmer's delicate and scientific tests. We publish the statement as a matter of interest to all who are interested in telegraphy.
DAVIDBROOKS: Dear Sir--I do not know how I can better set forth the value of your insulator than by showing what it will do on a No.9 iron wire with 30 posts per mile, in comparison with what other insulators in common use will accomplish. The average of No.9 inch wire in this country will weigh about 320 pounds per mile, and offers about 18 ohms or British Association units of resistance per mile.
The resistance which an insulator will offer to the escape of current from a line, depends upon the material of which it is made, and also upon the character and condition of its surface. If during bad weather an insulator retain much moisture upon its surface, although moisture is a poor conductor in comparison with iron or copper, yet it is an exceedingly good conductor in comparison with glass, porcelain, paraffine, &c., being perhaps a billion times poorer than copper, yet a billion of billion times better than glass.
A common glass and bracket insulator, in average condition upon a line, will in clear, cold, frosty weather, offer perhaps 10,000 megohms resistance more or less (a megohm equals a million ohms), but during a long continued rain this high degree of resistance falls sometimes as low as 9 or 10 megohms, and often lower-even below one megohm, but then it quickly regains a portion of its insulating power as its surface becomes dry. I presume from long experience, and many careful tests, made in the worst weather, that 9 megaohms will be above the average value of three quarters of the insulators used in this country, in the Middle and Northern States, in long continued heavy storms.
Some of your insulators, when new, will shows tests as high as 50,000 to 100,000 megohms, and that too in damp weather-and even after six or seven months' exposure they rarely fall below two or three thousands megohms. I have tested some as low as fifteen or sixteen hundred. The subjoined tables will show that so high insulation as this will enable the lines which use them to work to greater distances than have been hither to practicable.
Since a portion of the current leaks from a line at every insulator, it will come to pass that at some distance, depending upon the conductivity and insulation of the line, so much of the current will have escaped that what remains will be unable to affect the receiving instrument.
For example, take a No.9 iron wire, conductivity resistance 18 ohms per mile, 30 posts per mile, insulators of 4 megohms each, in worst weather; suppose the line 250 miles long, with way stations at 50, 100, 150 and 200 miles distance, only about 51 percent. of the entering current will reach the first station; 26-1/2 percent. reaches the second; 14 percent. the third; 8-1/2 the fourth way station, and 7percent. reaches the terminal station.
But if the insulators used be 9 megohm insulators, 69 percent. will reach the 1st, 49 percent. the 2d, 37per cent. the 3d, 30 percent. the 4th, and 28 percent. the terminal station. Nearly four times as large a proportion of the entering current reaches the far end with the 9 as with the 4 megohm insulators.
If now you should build lines of 50,100,150 and 200 miles in length, the terminal currents would be 93, 76, 57, 41, and 28 percent. of the entering currents for the 9 megohm insulator, but with the 4 megohm insulator they would be 81, 49, 26, 13 and 7 percent. These results I will throw together in tables No.1 and 2.
In order to show what distances can be reached by the use of different insulating powers, in a similar line, I subjoin table No.3, in which the second horizontal line shows to what distance one tenth of the entering current will reach with insulators of the several powers. At the head of the second, third, fourth and ninth columns, line third shows similarly to what distance ¼ of the current will reach; line 4th, same of ½ line; line 5th, same of 3/4 line; line 6th, same of 9-10.
Comparing the 8th and 9th column of this table with the second, third and fourth, will show more graphically to the eye, than words to the ear, what the Brooks Insulator can do.
Truly yours,
MOSES G. FARMER,
Consulting Electrical Engineer,
April 9th, 1869. Boston, Mass.
