September 11, 1885.] 



SCIENCE, 



207 



from the sun, and lie has determined the wave-lengths 

 of a newly discovered solar region by direct observa- 

 tion. We have in this infra red portion of the sun 

 spectrum the greater part of the heat which sustains 

 organic matter on this planet ; and the questions arise. 

 Does the planet radiate heat of the wave-lengths that 

 it receives from the sun ; and How is its temperature 

 maintained, probably several hundred degrees above 

 the temperature of space, when our observations 

 show that the direct radiations of heat from the sun 

 can only raise it about fifty degrees above the sur- 

 rounding temperature ? Experiments at Alleghany 

 show that the dark solar heat is transmitted by our 

 atmosphere with less difficulty than the light ; and if 

 the radiations of the soil are of this wave-length, our 

 planet should actually be cooler on account of its 

 atmosphere than if it had none. With this in view. 

 Professor Langley has carried on during the last two 

 years measurements of the radiations from bodies of 

 the temperature of our earth. Almost the only ma- 

 terial which can be used for the prism and lenses in 

 this work is rock-salt. It is needless to say that the 

 polish deteriorates after a few hours' use, necessitating 

 a constant resetting of the surface. Leslie cubes cov- 

 ered with lampblack, and filled with boiling water or 

 aniline, were used as radiating surfaces. Nearly the 

 whole heat spectrum from these sources passed 

 through the prism at angles which the theories of our 

 text-books have heretofore pronounced impossible. 

 Speaking with reserve. Professor Langley says that 

 we have every reason to believe that heat radiated by 

 the soil has a wave-length twenty times that of the 

 lowest visible line of the solar spectrum. Professor 

 Langley' s results are of interest to the physicist, as 

 showing that the wave-lengths of something more 

 than one two-thousandth of au inch are rendered 

 highly probable ; to the astronomer, because we find 

 that the heat radiated from the soil is of a totally dif- 

 ferent quality from that received from the sun; so 

 that the important processes by which the high sur- 

 face temperature of the planet are maintained, can 

 now be investigated with, we may hope, fruitful 

 results. 



Much of the success of Professor Langley' s work 

 depended on the possibility of making satisfactory 

 lenses and prisms from rock-salt. Professor Langley' s 

 paper was followed by one by Mr. J. A. Brashear, on 

 a practical of method working rock-salt surfaces for 

 optical purposes. Mr. George Clark succeeded in 

 making and polishing a rock-salt prism for Professor 

 Langley, but otherwise none had met with success; 

 and Professor Langley was assured by the best opti- 

 cians, that a rock-salt prism could not be made to 

 show the Fraunhofer lines. Mr. Brashear proved 

 this prediction to be false. Mr. Brashear's method 

 consisted in the use of a pitch bed, which, while yet 

 soft, was flattened by a plate of glass; the pitch was 

 then cooled by water, and upon it were drilled conical 

 holes one-quarter inch in diameter, and half an inch 

 apart ; the surface of pitch was then warmed suitably, 

 and upon it was pressed a true plain surface. Upon 

 the polisher thus prepared was put a very small quan- 

 tity of rouge and water. The polishing was done by 



diametrical strokes, the operator walking about the 

 polisher as he rubbed; this motion must be constant 

 and continued till the last traces of moisture disap- 

 pear, and the prism is to be slipped off the polisher in 

 a perfectly horizontal direction. 



Prof. H. S. Carhart presented a paper on surface 

 transmission of electrical discharges, which was an in- 

 genious revision of work by Professor Henry. Prof. 

 E. L. Nichols presented some further notes on the 

 chemical behavior of magnetic iron, a continuation 

 of work described in a paper at the Philadelphia 

 meeting. In the absence of Professor William Ferrel, 

 his paper on psychometry was read by title only. 

 Major H. E. Alvord of Mountainville, Xew York, 

 presented the results of telemetric observations at 

 Houghton Farm. This is a method by which changes 

 in temperature are transmitted and recorded elec- 

 trically; and Major Alvord' s results show that, with 

 increasing experience, the records followed more and 

 more satisfactorily the observations made on the mer- 

 curial thermometer. 



Commander Theodore F. Jewell's paper on the ap- 

 parent resistance of a body of air to a change of 

 shape, described some experiments at the U. S. torpedo 

 station, in which a disk of gun-cotton was exploded 

 on a metal plate. Upon each disk of the explosive 

 had been stamped the letters ' U. S. N.', and the year 

 in which the material had been manufactured. After 

 explosion upon the iron, similar indentations were 

 found upon the plate as if the air in the indented 

 letters had been driven into the plate. 



Professor T. C. Mendenhall called attention to the 

 modifications and improvements already made or de- 

 sired in electrometers, especially with reference to 

 their use in observations on atmospheric electricity. 

 Observations of this kind have been made regularly 

 for the last year or two ; but, as Professor Mendenhall 

 well said, the meaning of the variations recorded is still 

 a mystery. Prof. A. E. Dolbear read three papers: 

 in one he described a method of studying the contact- 

 theory of electricity by means of the telephone. He 

 has found that a click is produced in the telephone 

 every time the circuit is broken between two heter- 

 ogeneous materials, as copper and zinc. In another 

 paper he referred to his success in employing a Bern- 

 stein incandescent lamp for projection purposes; and 

 in the third he described a new galvanic element of 

 high electro-motive force and great constancy, con- 

 sisting of carbon in a saturated solution of bichro- 

 mate of potash and sulphuric acid, and zinc in a 

 saturated solution of ammonic chloride; nitric acid 

 could be used in place of sulphuric. Mr. A. J. 

 Kogers presented a paper on electrolysis of the salts 

 of the alkaline earth. 



It is much to be regretted that Prof. J. Burkitt 

 Webb was obliged, by want of time, to refer so 

 unsatisfactorily to his papers on entropy and the 

 life of the universe, in each of which he presuma- 

 bly discussed matters in the interest of thermody- 

 namics. 



Prof. E. L. Nichols has, by means of a spectro-pho- 

 tometer described at a previous meeting, compared the 

 spectrum of the unclouded sky with that of the light 



