Page:Science vol. 5.djvu/166

 [Vol. v., Wo. Ifll

��arm of oue of tlie men. The cost thus for is tl,188,000. The completed structure weighs 81,000 tous.

In this connection, some of the heights of notable atmctures may be of interest: Tower of Pisa, 179 feet; Bunker Hill monument. 221 feet; Great mosque, Cairo, 282 feet; Trinity spire, New York, 284 feet; Campanile, Flor- ence, 290 feet; top of capitol, Washington, 307 feet ; Milan cathedral, 355 feet ; St. Paul's, London, 3Go feet; Antwerp cathedral, 402 feet; Lutheran Mariankirche, Lubeck, 430 feet; St. Stephen's, Vienna, 441 feet; St. RoUox chimney, Glasgow, 450 feet; Great pjTamid, 450 feet (originally 485 feet) ; .St. Peter's, Rome. 455 feet ; Strasbourg cathe- dral, H)S feet; Cologne cathedral, 511 feet; Philadelphia city hall, to be 535 feet ; Wash- ington monument, 555 fect.

Many memorial stones were contributed by the states, and by different organizations in this country, and by foreign countries. Some forty of these stones were set in the interior faccs. One hnndred still remain in the store- house, and will probably be affixed as slabs to the interior walls in convenient places.

CHAKLVa E. GbEKNE.

��The recent experiments in England (iVuIwre, vol. XXX. p. 362), upon the i-elalive merits of electric, gas. and oil lights for lighthouse illumination, have called attention to the very marked failure of the arc-light to penetrate through a misty or foggy atmosphere ; this fail- ure being due to the \igorouH absorption of the blue raya of the spectrum by such an atmos- phere, — rays in which the arc-light is espe- cially rich. A very striking case of simitar failure was presented to the writer's notice a few evenings ago. One of the streets of Wash- ington has recently been lighted by arc-lights on each side, upon posts several feet higher than the gas-lamps; so that, in looking along the street, the rows of electric lights above the gas offer a good opportunity for comparison. For several nights both were lighted ; and one of these nights chanced to he extremely foggy for a few hours in the evening, the ground being covered with slush from melting snow. For Ihia reason I went out of my way to see the effect uiwn these lights, and was rewarded by the sight of the arc-lights — overpoweringly bright close at hand — becoming almost as

��faint and yellow as the gas-lamps at a distance of less than half a mile. The extent of the arc-lights was only five blocks, and the treasury building at one end, and patent office at the other, prevented a view from a greater dis- tance ; but there can be no doubt, that, if thej relative rates of absorption had continued isl the same ratio for a greater distance, the aro-' lights would have api^eared fainter than the gas-lamps at a distance of not much over half a mile, and would have entirely disappeared long before the latter. The arc-lights are said by the company to be of about two tliousand candle power, and the gas-lights probably equal between fifteen and twenty candles; so that the enormous difference of absorption under ^^ these circumstances is evident at a glance. To be sure, this was a very thick f<^ ; bat this is the very condition of things where peii&,. Irating power is most necessary for lighthouse lamps, and where the arc-light seems to fail utterly.

For search -lights, in naval warfare, as pro- tection against torpedo attack in thick weather, and for other similar pur|>o9es, the case is just as bad. or even worse : for the light must trav- erse llie necessary distance twice, — to the dangerous object, and then reflected back to the ship. For determining the best quality of light for submarine search, experiments upon the selective absorption of sea-water for vari- ous kinds of luminous radiant energy would seem to be desirable.

Professor Langley has shown, within the last year or two, that our atmosphere absorbs much more of solar radiant energy than has been heretofore supposed, and that this is very largely in the blue end of the spectrum ; so that sunlight, if we were rid of our atraoe- phera, would be much bluer than we see it. He has shown, too, that this Uikes place by diffusion of the light by reflection in all direi tious from particles in the atmosphere, so thst we get about half onr daylight from the sky, even in a perfectly clear daj- ; and that this is the cause of the blue sky.

The same ex|)lanation is sulllcient lo account for all the phenomena of the wonderful red afterglows following the sunsets of a year ago, if we can explain the presence of reflecting particles in a more or less stratified arrange- ment (Krakatoa dust, very likely) at an on- usual height in the atmosphere. Those would refiect sunlight to us in much greater amount and for much longer (semi-intermittent) inter- vals than the oi^iuary dust and clouds at a lower level of the atmosphere ; and this selec- tive absorption would account for the wonder*

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