OBSERVATION AND EXPERIMENT. The first of these terms ncludes a portion of the second, inasmuch as every experiment s made with a view of observing the reault. But experiment rignifies more than observation, implying a disposition of means if observation which it is in the power of the experimenter to make or himself, and which he actually did make for himself. If, for xample, a person who observed the attraction of the magnet for the irst time, dubious of the residence of the attracting power, were to nova the magnet to another place, that he might see whether the .ttracted body would atilt move towards it, he would make an experi neut. But if his magnet were the sun and the attracted body the arth, he could only wait the proper times for observing the motion of he latter with respect to the former, in order to establish the ttraction. Thus astronomy, geology, meteorology, natural history, cc., are sciences of observation (that is, of nothing but observation); vhilo mechanics, optics, electricity, &c., are sciences of experiment.
n one sense geology and meteorology are partly sciences of experiment, ince portions of the material subject-matters of these sciences may be ubmitted to preconcerted tests. It would, however, be more proper o consider mineralogy and aero-meehanics as the experimental sciences onnected with these, than to class them as mixed sciences.
To give an account of experiment would require us to explain the aethoda of every science which proceeds upon it : to give a detailed ccount of observation, we should need the description of all the means r instruments by which our senses are assisted in the examination of henomena. We shall here confine ourselves to a short sketch of the rrors which render observations discordant, and which make a final recess of combination necessary in every case in which we cannot ommand results which agree with each other so well that the difference etween them is imperceptible to the senses.
Everything which is called observation is of two kinds ; in the first simple individual fact is noted, in the second a magnitude is seasured. The results of the first species are the proper subjects of
eductive reasoning only ; the results of the second, of inductive and sathematical reasoning, either or both. Individually, tho first kind of bservations are not necessarily subject to error ; thus a zoologist baerviog the structure of a new animal might in every instance orrectly note the resemblances which exist between it and other nirnals, and might refer it to its proper class in a manner which snturies of succeeding observation would not induce naturalists to isturb. Collectively, however, wrong inferences might be drawn :out facts; thus results of classification which are true of all animals nown up to one moment, and aro therefore inferred to be always ale, may be disturbed -in tho next moment by tho discovery of a ew apocimen.
Observations of the mathematical character are of necessity crro ueous from the imperfections of our musses. When a new insect observed, it is soon peso, for instance, whether it has or has not wings, and the question once settled is finally settled. But when, say the specific gravity of a gaseous substance, at a even pressure and temperature, is serasaind, it is impossible to consider the question as settled at any time. Say that, tinder given circumstances, the specifie gravity is Asserted to be .934 of that of air similarly circumstanced ; this is only an admission, at mast, of its being somewhere between •9335 and .9345. And that which we call an exact measurement of a length may for one purpose mean within a hundredth of an inch, for another within a thousandth, and so on; but no person dreams of having attained absolute truth. This being well known, and every process' used in observation being subject to error, it is the business of the observer to repeat observations many times, and to'extract a result as Leer to the truth as TRAY be, from the male of discordant materials which the repetition will burnish.