462 Dr. G. Johnstone Stoney : Surrey of that pa rt of 



succeed in measuring are the distances of those few stars which 

 have perceptible parallax *. The distances of these stars from 

 the Solar System range from four to fifteen metro-sixteens ; 

 and it is not likely that any star could send us light enough to 

 be visible in any of our telescopes if a thousand times more 

 remote. At a distance, then, of about ten thousand metro- 

 sixteens — that is, at a distance of about a metro-twenty, our 

 knowledge of the starry universe comes to an end. It is 

 perhaps possible that the great Nebula in Andromeda, and a 

 few other non-gaseous nebulfe, are stellar systems distinct from 

 that of which the Milky Way is the outlying portion, and which 

 is commonly spoken of as the stellar universe. If so, such of 

 these other " universes " as can be visible to us probably lie 

 within a sphere which extends into the space beyond our stellar 

 system, perhaps some 100 times further than the boundary of 

 the Milky Way, and may accordingly need, to represent the 

 distances of some of them, numbers inserted in the next 

 column of our table (fig. 1). Accordingly, the column of 

 metro-twentyones is in the table indicated as one of those 

 included within the range of what man possibly already 

 knows something about. 



From this preliminary survey it appears that man is only 

 acquainted with a strictly limited portion of the scale upon 

 which the real operations of Nature are being carried on. All 

 her operations upon an ultra-stellar scale, all her activities at 

 infra-molecular degrees of proximity, are kept from our view 

 by tbat heavy veil of Isis which man's limited senses and his 

 restricted intellectual powers cannot lift. It raises us in the 

 scale of thinking beings to see clearly where our knowledge 

 must end, and to have ascertained definitely which part of the 

 boundless range of Nature's actual operations is that which 

 human powers are able to gauge and which human minds can 

 adequately grasp. The survey may be rendered definite with 

 the help of the table comprised in fig. 1, in which numerical 

 digits are to take the place of some of the ciphers. According 



* Attempts have been made to infer the parallax of binary systems 

 from a spectroscopic determination of the difference of velocity in the line 

 of sight of the constituent stars, combined with the known periodic time 

 and the apparent angular size and form of the system. This method has 

 been applied to y Virginia and to y Leonis with results which are not yet 

 free from doubt on account of the extreme delicacy of the observations, 

 but which seem to place these stars at distances, in the case of y Virginia 

 of about (JO metro-sixteens and in the case of y Leonis of 150. These 

 are distances which are one step of our scale farther, i. e. about ten times 

 farther, from us than those of which the parallax can be directly measured. 

 (See Astr. Nach. No. 3510, or < Nature ' for August 25, 1898.) 



