200 ANNUAL OF SCIENTIFIC DISCOVERY. 



the mirrors reflect the color. By means of certain arrangements, the 

 interposed glasses are made to produce effects aud combinations of 

 tints to which the rotation gives a fairy aspect. Where the light is 

 not colored, the reflecting power is said to be so great that a man may 

 read by it a kilometre's distance, about two-thirds of a mile. This 

 mode of lighting, it is added, may be turned to account for other pur- 

 poses than that of mere street illumination ; for example, for ship- 

 wreck signals, the lighting of great night works, tunnels, &c. 



VALUE OF THE BAROMETER IN NAVIGATING THE AMERICAN 



LAKES. 



At the American Association, Cleveland, a paper on the above sub- 

 ject was read by Mr. W. C. Redfield, of NCAV York. He commenced 

 by alluding to the great American lakes as remarkable, not more for 

 their extent and commercial advantages, than for the destructive 

 storms with which they are visited ; these storms being sudden and 

 the shores generally dangerous. The direct force of an easterly wind 

 on the Atlantic is seldom felt on the lakes. Every great storm, viewed 

 in its geographical extent, is a great cyclone, or eddying current of 

 wind. In these latitudes the first wind is from an eastern or a south- 

 ern quarter, preceded or attended by a fall of the barometer, phenom- 

 ena due to the northwesterly progress of the cyclone, and its leftwise 

 movement around its own axis of gyration. On the ocean these storm 

 winds can readily pass and act along the coast, but the varieties of land 

 surface prevent direct extension to the trans-alleghanian regions, and 

 lessens, also, the violence of the westerly winds which constitute the 

 westerly or closing portion of the cyclone. 



On the great interior plateau where the lakes are situated, these 

 conditions are partially reversed. The first winds of the cyclone here 

 blow from the eastern or southern board, and are impeded by the sur- 

 face of the country, and on the left side, the northwesterly winds, 

 which are retrograde to the advancing body or entire cyclone, are 

 necessarily less violent often quite moderate or gentle, compared 

 with the succeeding easterly winds. When the axial center of the 

 cyclone has passed the observer, the barometer, which has in the mean 

 time fallen to its lowest point, commences rising, the wind becomes 

 westerly, its force is suddenly and greatly increased, being a com- 

 pound of both the progressive and the rotative velocities ; these vio- 

 lent westerly winds are no doubt aided by the rapid and colder cur- 

 rent of the next higher stratum, which coincides in direction ; thus 

 these later westerly winds are almost inevitable as they sweep over 

 the lakes. 



A continual but varying series of these cyclones is passing over the 

 temperate and higher latitudes, producing variable winds. In the 

 North American cyclones, the first or advanced portion exhibits eas- 

 terly or southerly winds, the principal direction, locally considered, 

 being dependent upon the position of the observer laterally in its path. 

 These first winds produce a fall of the barometer ; the progress and 



