MECHANICS AND USEFUL ARTS. 103 



the American. One of the New York chronometers, in particular, 

 was subjected to the severest tests to which it is possible to subject 

 instruments of such delicate construction ; yet so exquisitely was it 

 provided with adjustments and compensations for the very great 

 extremes of temperature to which it has been subjected, that, having 

 suffered all sorts of exposure to which such instruments are liable in a 

 Polar winter, it was returned with a change in its daily rate, during a 

 year and a half, of only the eighteen thousandth part of one second in 

 time. In stating this fact it will be born in mind that the temperature 

 registered during the winter in Wellington Straits was actually 46 

 below zero. 



NEW ILLUMINATING APPARATUS FOR LIGHTHOUSES. 



A NEW illuminating apparatus for lighthouses, has been recently 

 brought out by Mr. Wilson, of Providence, and Dr. Meacham, of 

 Cincinnati. The improvement consists in a combination of the 

 dioptic and catoptic methods of illumination, and the arrangement of 

 the lamp and reflector is thus described in the Providence Journal : 

 " The lamp, which is of great illuminating power, has three concen- 

 tric wicks, the diameter of the larger" being 2f inches, with a 

 separate oil chamber for each, and to which, by a simple arrange- 

 ment of the conveying tubes, the oil is carried and constantly kept at 

 its proper level, thereby dispensing with the rack-and-pinion for 

 raising the wicks, as well as all the clock-work and pumps heretofore 

 found indispensable in lamps of this kind. 



The reflectors, which are arranged both above and below the light, 

 are constructed upon a die, the form of which is obtained by the 

 revolution of a parabola around an axis perpendicular to its OAvn, and 

 passing through its vertex ; and the diameter of the lamp and the 

 focal distance of the reflectors are so graduated to each other, that 

 the most luminous portion of the light shall always be in this univer- 

 sal focus. 



To prevent the escape of any radiant light, a cylindro-plano-convex 

 lens, having the same common focus, is placed 'between the middle 

 and lower reflectors, which transmits and refracts it in a line parallel 

 to a horizontal plane passing through the light. By this arrangement 

 all the light evolved is thrown out in a horizontal belt, and is equally 

 luminous or brilliant at all points. The cost of this apparatus is 

 about $300." 



SAFETY FLUID LAMPS. 







Two inventions have been brought out during the past year, 

 designed to obviate and prevent the frequent explosions of lamps 

 containing and burning the various fluids known as camphene, burn- 

 ing fluid, &c. These two inventions, by Prof. Hereford, of Harvard 

 University, and Mr. Newell, of Boston, are founded to a greater or 

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