ing a heavy load in a wagon weighing 3500 pounds over all grades met. The running time for the 201 miles was thirtythree hours, and at one point it made twenty-one miles in two hours and ten minutes, recording one mile in four minutes thirty-six seconds. In their report to the Governor the commissioners say: "The wagon has hauled loads, ploughed, and otherwise accomplished in a successful manner every test mentioned in the law or suggested by the commission. They are not, however, satisfied that this machine is, in the language and spirit of the law, a cheap and practical substitute for the use of horses and other animals on the highways and farms." The chief objection of the commissioners is understood to relate to the cost of operating the machine. The experimental trial, nevertheless, is universally conceded to have demonstrated a very decided advance in this field of invention.

TECHNOLOGY.

By WILLIAM H. WAHL, Ph.D.,
PHILADELPHIA, PA.

COMPARATIVE MERITS OF DYNAMO-ELECTRIC MACHINES. A most valuable and practical contribution on the subject of Dynamo-electric Machines was made during the last year by a committee of the Franklin Institute. The report of the sub-committee on Electrical Measurements, by Professors Houston and Thomson, is of such special value that its conclusions may be properly condensed in this place. The machines that were submitted to the comparative tests were a Gramme, a large Brush, a small Brush, and a Wallace-Farmer machine; and regret is expressed by the committee that it was not in their power to include a machine of the Siemens type (which lately received a very favorable endorsement from Professor Tyndall) in the list of those investigated. The conclusions reached by the gentlemen above named are, briefly condensed, as follows: The Gramme machine, considered as a means for converting motive-power into electrical current, is pronounced to be the most economical, giving a useful result in the arc equal to 38 per cent. (of power utilized), or of 41 per cent. after deducting friction. and the resistance of the air. In this machine the loss by friction and local action is the least, the speed being comparatively low.

The large Brush machine gave in the arc a useful effect equal to 31 per cent. of the power used, or, after deducting friction, 37 per cent. It is but little inferior, in this respect, to the Gramme, but has the disadvantage of higher speed, and consequently greater percentage of loss of power by friction. This loss, the committee note, is nearly compensated by the advantage possessed by this machine over the others of working with a high external compared with the internal resistance, thus assuring comparative absence of heating in the machine. The small Brush is ranked by the

committee as the third in efficiency, showing in the arc a useful result equivalent to 27 per cent. of the power employed, or of 31 per cent. after deducting friction. The committee state further concerning this apparatus, that although somewhat inferior to the Gramme, it is nevertheless admirably adapted for the production of intense currents, and has the advantage of being capable of furnishing currents of widely varying electro-motive force. It possesses the advantage of division of the conductor into two circuits, simplicity and ease of repair of the commutator, and comparative freedom from heating.

The Wallace-Farmer machine, according to the committee's report, does not return to the effective circuit as large a proportion of power as the other machines (14 per cent., or 15 per cent., deducting friction), although it uses in electrical work a large amount of power in small space. The cause of this low economy the committee attribute to the expenditure of a large proportion of the power in producing local action. They express the opinion, however, that by remedying this defect an admirable machine would be produced.

TELEGRAPHY.

In this department the progress made during the past year is specially noteworthy. The most prominent advances to be noticed are the invention of the microphone, by which minute sounds are rendered audible; the improvement of the phonograph, or talking-machine, the announcement of which invention was made in our last volume, but which was not practically brought out until the early part of 1878; and the considerable progress of the problem of electric lighting, which we have esteemed of sufficient importance to be given a separate consideration. The Telegraphic Journal, referring to the telephone, the phonograph, and the microphone, tersely defines their functions and utility as follows: "We have now a command over sound similar in kind to that which we possess over light. For the telephone is for the ear what the telescope is for the eye; the phonograph is for sound what the photograph is for light; and the microphone finds its analogue in the microscope." The last-named instrument has already received some highly useful applications, and as it is improved, and its capabilities are better understood, its utility

will doubtless be vastly extended. Sir Henry Thompson, and others following him, have successfully applied it in surgical operations and in medical examinations; Rosetti has employed it in the detection and observation of obscure seismic phenomena; and Houston and Thomson have applied it as a relay for the telephone. The utility of the telephone likewise has manifested itself in its extensive introduction into practical use; and we may note, as one of the most useful developments during the past year, the establishment of a system of telephone exchanges, by which a number of persons, who subscribe for the purpose, are brought into communication with each other through the medium of a central station.

The past year also witnessed the practical solution of the problem of duplexing submarine cables, by which their capacity for transmission has been materially increased; Muirhead's duplex system having been applied to the MadrasPenang section of the Eastern Telegraph Company's lines, and to that of the French Atlantic Cable, and Stearns having duplexed one of the Anglo-American lines. The quadruplex system, which was first introduced upon the postal telegraph system of England, in 1877, is reported to have proved so successful that it has been introduced upon additional circuits.

The gradual completion of the extensive net-work of underground cables, for some time in course of construction in Germany, to connect the principal cities of that empire, argues well for the success of the system in general. The latest information we have on this point gives the underground cable lines in Germany an extent of 2044 kilometers (1267.28 miles), in the following divisions: 1. Berlin, Halle, Frankfort-on-the-Main, with the branch lines, Halle-Leipsic and Frankfort-on-the-Main-Strasburg; 2. Berlin, Potsdam, Magdeburg, Cologne; with Cologne, Elberfeld, Bremen; and 3. Berlin, Hamburg, Kiel. The underground lines already laid are reported to give the utmost satisfaction; and the entire length of the lines that have been decided upon, and which are either at present in course of construction or will be shortly completed, is 16,121 kilometers (9995.02 miles). In this country the underground system-even in the cities, where their use is almost universal abroad-does not appear

to have received any attention, if we except the experimentaltrial of a short line of the Brooks system (covered wire conductors, laid in tubes, with paraffine oil as an insulator), in Philadelphia.

THE ELECTRIC LIGHT.

The scientific questions which of all others have attracted the most general and widespread popular interest during the past year are those pertaining to the improvement of the electric lighting systems and their possible adaptation for domestic purposes. One of the chief causes, doubtless, of the prominence attained by this subject, aside from its own merits, is to be credited to the fact of the introduction in Paris, during the period of the Exhibition just closed, of the electric light for the illumination of public squares, streets, gardens, halls, and places of amusement upon a scale not hitherto attempted; and the possibility that the rapid improvement of the electric light, which will reasonably be expected to follow upon the efforts of the numerous inventors who are engaged in the effort to solve the problem of adapting it for general illuminating uses as a substitute for gas, might soon be crowned with success, has caused much uneasiness among the gas fraternity, whose important vested interests, it is feared, would in consequence suffer serious depreciation in value. From all that can be learned, however, the difficulties that surround the problem of adapting electric lighting to domestic uses, as a practical substitute for coal-gas, are of such a serious nature that their removal, although it may be successfully accomplished sooner or later, is scarcely to be expected as an event of the immediate future. Upon the question of the relative cost of the electric light as compared with gas, the comparison being based upon the quantity of light produced, the electric light has decidedly the advantage of the other. In point of purity likewise it is incontestably superior to gas, over which it possesses other and important hygienic advantages. There are other qualities, however, equally important, which the electric light must be demonstrated to possess before it can figure as a rival to present methods of domestic illumination. It must be susceptible of perfect subdivision. The dazzling glare and intensity of the electric light in its present form, while it may be manageable in large open spaces, halls, factories, and public buildings, where it