620 



SCIENGE. 



[N. S. Vol. III. No. 69. 



poorer nights. The average probable error 

 of the parallaxes of Table I. is ±0."046, 

 and, therefore, the true values should be 

 within one-tenth of a second of the numbers 

 there given. When we consider average 

 values of parallax, however, we have a 

 more trustworthy determination of the dis- 

 tance of certain stars as a class. Thus ten 

 stars of the list have a proper motion of one 

 second or more. The mean value of their 

 parallaxes is +0."11, with a probable error 

 of ±0. "015, so that the average distance of 

 these stars is indicated to be such as to re- 

 quire about thirty years to be traversed by 

 light. Table I. contains one star, Lalande 

 ^7019, which found entrance quite unex- 

 pectedly. It was the first comparison star 

 for 85 Fegasi, and the latter was first reduced 

 in the regular manner but showed a nega- 

 tive parallax. This was explained upon 

 making comparisons of the first star, Lalande 

 47019, with S3 Fegasi and the third star of 

 the group separately, for the two solutions 

 resulted in positive and nearly equal values 

 of the parallax for the first. The mean of 

 these two values, +0."21 and +0."27, is 

 given in the table. An inspection of the 

 data indicates that this is a real parallax, 

 and not merely an apparent one such as 

 might be ascribed to personal change. The 

 magnitudes of the stars were 8.1, 6.1, 6.2 

 respectively, and no screens were employed 

 in this group. I included in the examina- 

 tion a number of observations made with 

 the screens expressly as a control on the 

 personal equation depending upon the bright- 

 ness of the stars. The case of Lalande 

 4-7019 is an interesting one, since the star 

 is faint and the comparison of four catalogue 

 positions extending from 1800 to 1890 gives 

 no plain indication of proper motion. Yet 

 the results indicate that it is the nearest 

 star of the thirteen in the table. With this 

 separate presentation of Lalande 47019 and 

 85 Pegasi, it will be noticed that while some 

 of the parallaxes are very small yet they 



are all positive. According to the law of 

 chances some of these values should be the 

 lowest possible ones derivable for the indi- 

 vidual stars and some should be the highest 

 possible values. The fact that they are all 

 positive and comprised within so limited a 

 range indicates that the observations are 

 not liable to such systematic errors as have 

 even led sometimes to large negative values 

 of parallax, and strengthens the hypothesis 

 that the stars of large proper motion are 

 on the whole comparatively near us. 



In the case of two of the stars we 

 have several independent determinations as 

 shown in Table II. For vj Cassiopeice, one 

 of the stars having a remarkably large 

 proper motion, the results indicate a defi- 

 nite parallax of about 0."13. The number 

 of separate determinations, however, is few, 

 and we can only say that the chances are 

 that the distance of this star is such that it 

 requires somewhere from 22 to 30 years for 

 its light to reach us. « Lyrce has been a 

 favorite object for parallax observations, 

 owing to its brilliancy and its favorable 

 position for northern observatories, and 

 consequently we have a good determina- 

 tion of its distance. The concluded value 

 of the parallax, +0."138, corresponds to a 

 light journey of 23.6 years, and the uncer- 

 tainty of this result is so small that the 

 chances are that the time actually required is 

 somewhei-e between 22.3 and 25.1 years, 

 while we may feel confident it cannot be 

 more than 33 years nor less than 18 years, 

 that its light requires to reach our system . 

 A. S. Flint. 

 Washbukn Observatory, Madison, Wis. 



OZARKIAN EPOCH— A SUGGESTION. 

 Among the voluminous writings on vari- 

 ous geological subjects published during the 

 past ten years, there has been frequent men- 

 tion made of an erosion interval occurring 

 between the Lafayette formation and the 

 lowermost glacial deposits. Those who 



