110 MODES OF MEASURING MINUTE INTERVALS OF TIME. 
fluence of the first, or the special constitution of the observer, was, until lately, almost en- 
tirely overlooked. The improvement, however, of instrumental measures in these later 
times has brought it prominently forward, as one of the most influential elements affecting 
the accuracy of astronomical observations. Every thing, therefore, which can reduce the 
amount of uncertainty due to it, or which tends to eliminate altogether its effects, becomes 
of high importance. 
To understand the limit to which uncertainty in observations may be diminished, in 
so far as it is dependent on personal equations, requires that we should analyze sensation 
and thought in their relation to time. Every one feels that both are conditioned to time; or 
that the changes of sensation and of thought do require a certain duration, so that, though 
rapid compared with many phenomena, they are slow compared with others. We must 
not confound the special differences in character, nor the physical distances in position, 
between the objects imaged by the presentative faculty of the mind, with the length of 
interval in time expended in the change. When our thoughts go from a line in the 
Odyssey to the ocean which it recalls, or from the diamond spark on a beetle’s wing-case 
to the twinkling of the pole star, thought is not more rapid than in proceeding from the 
beetle’s limb to his eye, or from one word to the adjoining one. The real velocity of 
thought consists in the number of changes which are possible in a given time. It does 
not follow from any thing known a priori as to a spiritual nature, that this velocity should 
be indefinite; or, in different orders of spiritual nature, should not follow different defining 
laws; except that in the highest or creative intelligence, thought must be timeless, abso- 
lute and without succession. It belongs to our connexion with material things, that thought 
should have a relation to them and to their movements, for these movements constitute 
and measure time to us. Whether changes of thought, or changes of sensation, be the 
more rapid, is an interesting question. ‘The comparisons which it suggests, show plainly 
the fact, that thought is conditioned to time, and serve also, to some extent, to determine 
the condition. 
An impression of light occurring oftener than ten (10) times in a second of time, will 
to most eyes appear a continuous illumination. Impulses of sound beyond (16) sixteen 
in a second, will not generally be apprehended as distinct sounds. In regard to neither 
sense do I, of course, speak at present of the physical vibrations which put our organs 
into a sentient state, but of the continuance of that state when it is produced in the sentient 
organ. It is the termination of this state which constitutes the change of sensation. The 
number of such changes in a given time is its velocity. We reckon therefore that the re- 
lative velocities in regard to sensations in the eye and the ear, are as 10: 16. No ideas 
in the mind are perhaps simpler than those of number, in whatever mode, or under what- 
