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��fill color, the light growing redder Lhe rarlher it traveraed the stmosphi^re.

In B recent article ' Professor Lauglej' states his belief that much of this dilTiisioii of the blue rays, as also the general absorption of the whole spectrum, is due to fine dust-parti- clea in the atmosphere. The very strong nb- SorpttOD of the blue raya of the arc-light by

1 would seem to suggest the inquiry whether t average size of the minule water-drc^s ming this fog lias any thing to do with the markably selective eflcct upon the blue wave- engths, or whether this is simply the absorp- tion effect of water eti masse.

With the failure of the arc-light to penetrate to^ comes the natural inquiry, whether the incandescent lamp will be any better for light- bouse and search-ligbt purposes. Now, the part of the solar spectrum moat free from at- mospheric absorption -lines ia in the orange, with part of the neighboring yellow and red; and some experiments hare shown that this re- gion — or the yellow part of it, at any rato — is 'bat in which the incandescent carbon filament i especially rich, relatively more so than the lar spectrum, and it is the brightest part of _, at. So that there would seem to be every probability that the incandescent lamp would prove very effective in fog penetration, perhaps it efficiently so at a slightly lower tempera- (nre and brillionoy than the present average, "^e difficulty for lighthouse and search-light prposea would be in concentrating a sufficient mount of luminous radiating filaments in a ery small space near the focus of a lens or lirror, which is a strong point in the effective use of the arc-light. With single- filament lamps this would be impossible; but the writer ' isuperable difficulty in arranging I whole bunch or cluster of interlacing loops, liriDed in multiple arc within the same ex- Musted globe, so as to present almost a com- plete network of filaments over a vertical projection of an inch or two square, and yet not have them touch each other; unless, in-, the great heat might soften the globe tough to let it collapse; and this could prob- ftily only be determined by experiment. The jgestion that a slightly lower temperature 'might be about as effective in f<^ penetration would help a little, but not very much, on ac- count of the rapid decrease of luminosity, with I alight fall in temperature. Special care would Ked to be taken to make each of the filaments H the cluster of equal resistance with the Hlicrs; but no more so than in any set of pmps on the same circuit, and no doubt all

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��the difficulties could be speedily surmounted. Some experimeuts upon the fog- penetrating power of the incandescent lamp would cer- tainly seem to be worthy the attention of those engaged in these matters; for there can l>e no question about the far greater convenience, cleanliness, safety, and reliability, of the in- caudesccnt lamp over all othei-s, eveu if it is not so economical. But in government light- houses and war-ships the economy is not so im- portant, reliability and fog- penetrating power being the prime requisites. H. M. Paul.

��RECENT DETERMINATIONS OF LON- GITUDE ON THE WEST COAST OP SOUTH AMERICA.

The recent completion of the longitude measurements on the western coast of South America by the U. S. naval officers, under the command of Lieut. -Commander Charles H. Davis, U.S.N., affords a remarkable proof of the accuracy of the methods and instruments now in use for such operations. Lieut.-Com- mander Davis commenced his measurement in November, 1883, at Valparaiso, and ter- minated it iu March, 1884, at Panama; con- necting there with the chain of measurements made in 18T.J by Lieut. -Commander F. M. Green, U.S.N., and measuring from Valparaiso to Arica, Arica to Payta, Payta to Panama,' and in December, 1883, with the aid of Dr. B. A. Gould, director of the Cordoba obser- vatory, from Valparaiso to Cordoba. This work completes the telegraphic measurement of the polygon Washington- Key West, Key West^Havana, Havana-Santiago de Cuba, .Santiago-Kingston, Kingston-As pin wall. As- pi n wall-Panama,' Pauama-Payta, Payta^ Arica, Arica-Valparaiso, Valparaiso-Cordoba, Cordoba-Buenos Aires, Buenos Aires-Monte- video, Montevideo-Rio de Janeiro, Rio de Janeiro-Bahia, Bahia-Pernambuco, Pernam- buco-St. Vincent, St. Vincent-Madeira, Ma- deira-Lisbon, Lisbon-Greenwich,' Greenwich- Washington.*

This great chain of longitude measure- ments, consisting of twenty links, closes with but an insignificant discrepancy; the longi- tude of the Cordoba observatory by way of Lisbon, Rio de Janeiro, and Buenos Air«s, being 4h. 16m. 48.06s.,andby way of Wash-

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