SCIEACE.
��Dk. Kkxst Hagen. professor of applied pbfsics in the Royal pohtechnif school of Dreadeii. visited the llnited Slates in 1884. and, haTing carct^iUy examined the difTerent systenis of electric lighting there in to^ic, pre- sented X report to the dii'eclors of public build- tngB of Berlin. The lai^est portion of this report is devoted to the subject of incandescent lighting. A certain space is given to accumu- kilora, and arc-lighting is also considered. The writer states in his prefnee that his travels have doeponed in him the conviction that the suh- diviflioD of the electric light by means of the nefbei-AItemeck dilffrential lamp gives a greatei' degree of steadiness than is possible with tlio lamp of any of the American syslems.
The author enters at first into a comparison of the cost of electric lighting in gencrul with Hint of gns and other sources of light. lie shows lliiit ncnrli' ninety i>er cent of the enet^y prodnceil by the ordinary gas-flame is in the form ofhc.it, leaving only aiiout ten percent in the form of the radiations which ap|»eal to ns as light. He also diacusscs the subject of the iiosious gaees given off by illuminating- gas. and the poisonous compound called by Dnliois- Ri-yroond ' anihropotoxin.' which accompanies Uie carl ionic- acid gas, and finds much to con- demn in the use of illuminating-gns, and much good to expect in the Rirlher extension of the incandescent ^yslem of electi'ic lighting. When amount of light and health are considered, the
wndeecent system is economical: viewed n the point of dollars and cents, however.
bcannot be proved.
lie author gives a »hoi't history of the de- _iuent of the dynamo-uiachiiic, and the
per will find hero a better summary than in
f aimilar work with which we are acquainted.
B use of diagrams and modest engravings,
1 of the full-page illustrations of many
mt treatises, is especially relVeshing and
fcforling to one's pocket. The head is fille<i, B Uie )>oeki.'t is not depleted, which cannot aid if one buys most treatises on electric Bng-
l»e learn IVoni the chapter on the incandes- &t light, that Swan and Edison came almost simultaneously to the invention of the carbon- Ulainent lamp, which. indee<l. had been used in an iin|)erfect way hy inventors long before tliem. Hotli Swan and Kdison readied the
��' IHt tldiMKlir btlncMnne
�� ��result of a more or less permanent incandes- cent lamp in 18T9. The writer closes his his- tory of the incandescent lamp by a glowing eulogy of the man who had the genius to create a new industry which employe hundreds of workmen, and to conceive of the grand project iif lighting bj- electricity a great city from a central station. That this could have been accomplished without the careful training of the Gci-man polytechnic schools, evidently im- presses the author.
Dr. Ilagen corrects the impression, which is evidently carried abroad in certain quarters, that the whole of New York is lighted by the Rdison system. He computes that New York projier covers eleven square miles, and the [jortion lighted by Edison embraces only a tenth of a square mile, and covers an area comprised within a circle of a little less than a thousand feet radius. A map of the region covered by this sj"stem in New York is given; and the dimensions and construction of the main lending wires, and the method of insulating Ibeni in underground pijies, arc fully described, with a nmning criticism of the results that have l)een attained.
It is the author's opinion that large ccutral electric -lighting stations will be established in all great cities, if the esperiment in New York does not show some at jiresent unfore- seen obstacles. The system of underground wires forms, in his opinion, ouc of the greatest obstacles. There is no doubt that the insula- tion grows worse with time, and it is a question how much of the electrical energj- is lost by defective insulallon. lie very prop- erly remarks that the entire resistance of the circuit, including of course the lamps, must be considered, together with the loss of insu- lation in the underground conductors, and that even a very large loss of insulation might not consume more electrical energy than a single lamp.
The Edison plant is then carefully described, and the dimensions of the various machines Ailly given, together with the means of regu- lating the current, the method of weighing it and distributing it. We do not know whereto look for a more caref\il description of the con- struction of the underground cables and the method of insulation. The author concludes, that, for equal amount of light, the Edison hght costs about a third more than gas. In spite of this increased expense, the numlwr of sub- scribers has continued to increase since the opening of the system, .Sept. 3. 1883, and great satisfaction has been expressed with the light. Whether the system is suitable for
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