32 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 92 



place on scores of plates taken for years together without feeling an 

 absolute certitude of their real existence as regions of special absorp- 

 tion in the solar or terrestrial atmosphere. After longer study it is 

 found that as absolute a certainty exists as to many hundred smaller 

 lines seen in the same conditions, and yet as we improve our appara- 

 tus and recognize still minuter solar deflections, we finally come to a 

 condition where these are reduced to the same order of magnitude as 

 those which may be due to earth tremors and to similar accidental 

 disturbances, which are here represented by the irregular line which 

 is called the ' battery record.' 



" But, it may be asked, are we not entitled to demand that these 

 last should somehow be eliminated altogether and the ' battery record ' 

 become a perfectly smooth line? The answer is, that this can never be. 

 "As seismography improves, it becomes more clear that there is no 

 part of the earth's surface free from constant tremor ; as the refine- 

 ments of electrical science advance we constantly discover earth cur- 

 rents where they were not perceived before ; as we multiply the sensi- 

 tiveness of our measuring apparatus, till it comes to what seems almost 

 indefinite delicacy, we find that the most massive apparatus and the 

 most refined precautions which we may take, do not prevent the exis- 

 tence of all but infinitesimally small accidental disturbances, nor of 

 the notation of their sensible effects if the record itself be only minute 

 enough, for this record is a testimony, in fact, to the sensitiveness of 

 the apparatus itself, and minute distur1)ances are always to be found 

 if the observation itself which deals with them provides in itself the 

 means of detecting them. 



" It fell to the writer once to establish a permanent meridian instru- 

 ment whose supports he desired to build up with every condition of 

 stability which experience and caution could suggest. He personally 

 looked to the obtaining of the required blocks of granite at the quarry 

 and to laying them in the same way in the foundation of the observa- 

 tory on its bed rock as they lay in the original bed, and he super- 

 intended the placing of those, one upon the other, until the foundation 

 was laid for the piers which finally supported the instrument, and 

 which were chosen with the same care. He believed that this instru- 

 ment was as solidly mounted as anything on the earth could be. He 

 used it for many years in his observations with a confidence justified 

 by the results ; but these observations required a powerful telescope, 

 and there was no time at which a tap of the fingers on the side of 

 the monolothic piers which carried the telescope w^ould not be accom- 

 panied by an apparent leap in the heavens of the star on which it 



