It has been said,[6*] that if we had but one sensation, {41} and that uninterrupted, it would be as if we had no sensation at all; and, to the justice of this observation, some very striking facts appear to bear evidence. We know that the air is continually pressing upon our bodies. But, the sensation being continual, without any call to attend to it, we lose, from habit, the power of doing so. The sensation is as if it did not exist. We feel the air when it is in motion, or when it is hotter or colder, to a certain degree, than our bodies; but it is because we have the habit of attending to it in those states. As the muscles are always in contact with the same things, the sensations of the muscles must be almost constantly the same. This is one reason why they are very little attended to, and, amid the crowd of other feelings, are, in general, wholly forgotten. They are of that class of feelings which occur as antecedents to other more interesting feelings. To these the attention is immediately called off, and those which preceded and introduced them are forgotten. In such cases the thought of the less interesting sensations is merged in that of the more interesting. [Mill's footnote 6: Itaque et sensioni adhæret, proprie dictæ, ut ei aliqua insita sit perpetuo phantasmatum varietas, ita ut aliud ab alio discerni posset. Si supponeremus, enim, esse hominem, oculis quidem claris cæterisque videndi organis recte se habentibus compositum, nullo autem alio sensu præditum, eumque ad eandem rem eodem semper colore et specie sine ulla vel minima varietate apparentem obversum esse, mihi certe, quicquid dicant alii, non magis videre videretur, quam ego videor mihi per tactûs organa sentire lacertorum meorum ossa. Ea tamen perpetuo et undequaque sensibilissima membrana continguntur.--Adeo sentire semper idem, et non sentire, ad idem recidunt. _Hobbes_, _Elem. Philos._ Pars IV. c. xxv. § 5.--(_Author's Note_.)]