THE PROGRESS OF SCIENCE. 



287 



toniadi and others, found on photo- 

 graphs of the star a halo, which did 

 cot appear about other stars on the 

 same plate, and which was thought to 

 be nebulous. Later it was shown by 

 Professor Max Wolf that this aureole 

 was instrumental, and due to the fact 

 that the Nova was rich in rays for 

 which the lenses were uncorrected. At 

 the same time Wolf found that the 

 Nova was surrounded by a faint 

 nebulosity. Long exposures with the 

 powerful reflecting telescopes of the 

 Yerkes and Lick Observatories showed 

 well this nebulosity, and, especially, 

 nebulous patches at considerable dis- 

 tances from the Nova. From later 

 photographs it was announced from the 

 Lick Observatory and confirmed at the 

 Yerkes Observatory, that these nebu- 

 lous masses are moving away from 

 the Nova. This is a discovery of the 

 highest importance, having a direct re- 

 lation to the theory of new stars. The 

 motion of the nebula is very great, 

 amounting to about 1' of arc in six 

 weeks. Carried backward this motion 

 would bring the nebulous masses at the 

 Nova, when the outburst occurred, a 

 fact of much interest. What this rate 

 of movement represents in miles per 

 second cannot be assumed safely until 

 the star's parallax is known. This has 

 not yet been determined. Our nearest 

 neighbor among the stars, so far as 

 known, has a parallax of less than 1". 

 A parallax as great as 1" would indicate 

 a velocity of something like 1,500 miles 

 per second. Either the Nova is very 

 near us, or else the velocity of the 

 Nebula is almost inconceivably great. 

 Indeed, if the parallax should prove to 

 be too small for measurement, the fact 

 would imply a velocity so great that it 

 might be better explained as a motion 

 of light, rather than of matter. The 

 motion, moreover, appears not to be 

 radial, but spiral. The broadening of 

 the lines of the spectrum of the Nova 

 furnishes a clue to the rapidity of 

 motion, the value of which is, however, 

 very doubtful. No definite conclusions 



can be safely drawn until more data arc 

 obtained, and a satisfactory determina- 

 tion of the parallax is given. Mean- 

 while the astronomical world is watch- 

 ing the developments mth the keenest 

 interest. Incidentally the investiga- 

 tion is furnishing a powerful argument 

 for a more extended use of large re- 

 flecting telescopes. It may be, that the 

 Golden Age of the refracting telescope 

 has passed! 



THE MAGNITUDE AND THE MASS 

 OF THE VISIBLE UNIVERSE. 



An interesting question which often 

 occurs to the astronomer and the 

 physicist is that of the magnitude and 

 the material contents of the visible uni- 

 verse. While science is unable at pres- 

 ent to give a decisive answer to this 

 question it is nevertheless competent to 

 correlate the observed facts to such an 

 extent that a possible, if not a prob- 

 able, answer is already attainable. The 

 latest contribution to this subject is 

 due to the indefatigable labors of Lord 

 Kelvin. In the ' Philosophical Maga- 

 zine' for August, 1901, he attacks the 

 question from the dynamical side in an 

 article 'On ether and gravitational 

 matter through infinite space'; and at 

 the September meeting of the British 

 Association for the Advancement of 

 Science he amplified his investigation 

 in a paper on 'The absolute amount of 

 gravitational matter in any large vol- 

 ume of interstellar space.' 



The data for Kelvin's investigation 

 are as follows: The part of the uni- 

 verse visible to us may be considered to 

 lie within a sphere having a radius 

 equal to the distance of a star whose 

 parallax is one thousandth of a second 

 of arc. This distance is about thirty 

 thousand million million kilometres; a 

 distance so great that light would re- 

 quire about three thousand years to 

 traverse it. The number of stars, 

 luminous and non-luminous, within 

 this sphere, Kelvin estimates to be 

 something like one thousand million. 

 This agrees well with the figures of 



