96 Chronicles of Science. [Jan., 



The discovery of a small comet by the indefatigable Tempel 

 has to be recorded. No observations of special interest have been 

 made upon this object, however. 



The November meteors have not been very conspicuous in 

 Europe, this year. Unless we hear of star-showers in America, we 

 must conclude that the denser part of the meteor-stream has now 

 passed completely away from the neighbourhood of the earth's 

 orbit. In that case we need not look for any remarkable display of 

 the November meteors for some twenty-eight years or so. 



Zollner, the eminent photometrician and astronomer, has devised 

 a new form of spectroscope for observing the stellar motions of re- 

 cess and approach. The plan may be briefly described as follows : — 

 The line of light which is to be analyzed by the spectrum is in the 

 focus of a lens for parallel rays. These parallel rays are divided 

 into two portions, each passing through two systems of direct-vision 

 prisms, placed one below the other, and with their refracting edges 

 turned in opposite directions. It is clear that by this arrangement 

 two spectra are formed, the red end of one opposite the blue end of 

 the other, and vice versa. These spectra are observed together by 

 means of a small telescope, the object-glass of which is divided into 

 two adjustable parts by a line parallel to the length of the two 

 spectra. It is thus possible to bring any line of one spectrum into 

 coincidence with any line of the other, or even partially to superpose 

 two hues. Xow it is clear that if a celestial object is moving from 

 or towards us at such a rate as to produce an appreciable effect 

 on the position of a given bright line, Zollner 's arrangement will 

 exactly double the effect. This, however, is not the chief advantage 

 of the arrangement. In fact this is, in reality, no advantage at all 

 (though Zollner appears to think differently), for it is obtained by 

 an arrangement which halves the light of the spectrum ; and by 

 simply doubling the dispersive power the same increase of effect 

 could be obtained at exactly the same cost. The great advantage 

 promised by the new arrangement is this, that there will be no 

 occasion to compare a line directly with the corresponding line of 

 a terrestrial element. Thus, supposing we wish to determine whether 

 a star is moving from or towards the earth, by observing a particular 

 dark line in its spectrum, we should in the first place adjust the 

 two spectra so that this line seen in one would be brought into 

 coincidence with the same line seen in the other, supposing there 

 were no motion of recess or approach. This can be done with great 

 nicety by observing the corresponding bright line of a terrestrial 

 element. Then the telescope being directed towards the star whose 

 motion is to be determined, there will be found no longer to be 

 coincidence, if the star is in motion either from or towards the eye. 

 By observing how much the micrometer screw by which the divided 

 object-glass is adjusted has to be moved in order to secure coinci- 



