188 CHARLES BABBAGE. 



This desire for extreme accuracy has called away the attention of ex- 

 perimenters from points of far greater importance, and it seems to have 

 been too much overlooked in the present day that genius marks its 

 track, not by the observation of quantities inappreciable to any but the 

 acutest senses, but by placing !N"ature in such circumstances that she is 

 forced to record her minutest variations on so magnified a scale that an 

 observer, possessing ordinary faculties, shall find them legibly written. 

 He who can see portions of matter beyond the ken of the rest of his 

 species confers an obligation on them by recording what he sees 5 but 

 their knowledge depends both on his testimony and on his judgment. 

 He who contrives a method of rendering such atoms visible to ordinary 

 observers communicates to mankind an instrument of discovery, and 

 stamps his own observations with a character alike independent of tes- 

 timony or of judgment. 



On the Art of Observing. 



The remarks in this section are not proposed for the assistance of those 

 who are already observers, but are intended to show to persons not 

 familiar with the subject that, in observations demanding no unrivaled 

 accuracy, the principles of common sense may be safely trusted, and 

 that any gentleman of liberal education may, by perseverance and atten- 

 tion, ascertain the limits within which he may trust both his instrument 

 and himself. 



If the instrument is a divided one, the first thing is to learn to read 

 the verniers. If the divisions are so fine that the coincidence is fre- 

 quently doubtful, the best plan will be for the learner to get some ac- 

 quaintance who is skilled in the use of instruments, and, having set the 

 instrument at hazard, to write down the readings of the verniers, and 

 then request his friend to do the same. Whenever there is any difference, 

 he should carefully examine the doubtful one, and ask his friend to point 

 out the minute peculiarities on which he founds his decision. This 

 should be repeated frequently, and, after some practice, he should note 

 how many times in a hundred his reading differs from his friend's, and 

 also how many divisions they usually differ. 



The next point is, to ascertain the precision with which the learner 

 can bisect an object with the wires of the telescope. This can be done 

 without assistance. It is not necessary even to adjust the instrument, 

 but merely to point it at a distant object. When it bisects any remark- 

 able point, read off the verniers, and write down the result;- then dis- 

 place the telescope a little and adjust it again. A series of such observa- 

 tions will show the confidence which is due to the observer's eye in bisect- 

 ing an object, and also in reading the verniers; and as the first direc- 

 tion gave him some measure of the latter, he may, in a great measure, 

 appreciate his skill in the former. He should also, when he finds a de- 

 viation in the reading, return to the telescope and satisfy himself if lie 

 lias made the bisection as complete as he can. In general, the student 



