PHYSICAL AND MATHEMATICAL SCIENCES. 131

tion upon the plane, he conceived this chain will alwayssustain itself at rest; the part below cannot affect itsmotion. Hence the parts on the plane and in the per-pendicular support each other, and their weights areproportional to those lengths respectively.

These investigations entitle Stevin to be regarded asthe father of modern statics. After the inclined planehad thus been investigated, various other authors com-pleted the different parts of the subject by following upthe conclusions resulting from the principle of resolutionof forces.

To Stevin we likewise owe the first suggestion of thefundamental principle of hydrostatics, that the pressureof fluids is in proportion to their depth.

The rainbow had from the earliest times been an ob-ject of admiration to every spectator, hut it was longbefore any observer knew the full extent to which thatadmiration ought to be carried, or even cared to under-stand it. If it he unpardonable to shut our eyes to themost glorious spectacles in nature, it is doubly so toclose our mental vision against that more perfect andmore intimate perception of them, which the knowledgeof their causes affords.

Among those who felt any interest in such enquiries,the rainbow was generally understood to arise in someway from the light reflected by the drops of rain fallingopposite to the sun.

Maurolycus suggested that the light in passing throughthe drop, so as to be reflected from its back, somehowacquires colour from the refraction. But he proceededno farther with this idea. Others made suggestionswhich only tended to perplex the matter.

Antonio de Dominis, archbishop of Spalatro, ap-proached very nearly to the complete explanation. Hav-ing placed a globular bottle of water opposite to the sun,and above his eye, he saw coloured rays issue from theunder side of the globe; the colours were different,according as it was more or less elevated; and in theorder of the rainbow. He correctly traced the course ofk 2