.EXPLANATION OF SCIENTIFIC TERMS. 



13 



RATIO. In comparing two subjer's, -with 

 regard to some quality which they ha\ < 

 in common, and which admits of being 

 measured, that measure is their ratio. 

 It is the rate in which one exceeds the 

 other. Proportion is the portions, or 

 parts of one magnitude that are con- 

 tained in another. When the ratio is 

 commensurable, (that is, when it is redu- 

 cible to numbers,) it is equivalent to pro- 

 portion ; but the latter term is usually 

 employed in the comparison of ratios, in 

 which case, two equal ratios are said to 

 be proportionals. Thus 3 has to 4 (written 

 3 : 4) a certain ratio, or .proportion ; but 

 the expression 3 is to 4 in the same pro- 

 portion as G to 8, denotes that the ratios 

 of 3 to 4 and G to 8 are equal ; 3 being 

 the same proportion of 4 as 6 is of 8, that 

 is, three-fourths. Ratios, however, may 

 be unequal. Thus it is said that the 

 ration of 9 to 4 is greater than that of 

 7 to G, because | is greater than | : it 

 being thus that ratios are measured. 



DIRECT AND INVERSE. 



When two quantities, or magnitudes, 

 have a certain ratio to each other, and 

 are, at the same time, subject to increase 

 or diminution; if, while one increases, the 

 other increases in the same ratio, or, if 

 while the one diminishes, the other dimi- 

 nishes in the same ratio, the proportions, 

 or comparisons of ratios, remain unal- 

 tered, and those quantities, or magni- 

 tudes, are said to be in a direct ratio or 

 proportion to each other. Thus, if a 

 yard of cloth be worth a pound, ten or 

 any number of yards will be worth so 

 many pounds, and the proportion of value 

 continues unaltered. 



But, if the magnitudes are such, that, 

 when one increases, the other necessarily 

 diminishes ; and vice versa, when the 

 one diminishes the other increases, the 

 ratio, or proportion, is said to be inverse. 

 Thus, there is, at any moment, a certain 

 ratio of the length of the day to that of 

 the night; but this is an inverse ratio; 

 for, in proportion as the length of either 

 increases, that of the other must diminish. 



RATIO, Compound. A compound ratio is 

 made up of the product of two, or more, 

 simple ratios ; that is, of the product of 

 their first terms, which are called Ante- 

 cedents, compared with the product of 

 their second terms, called Consequents. 

 Thus 24 : 3 is a compound ratio of 4 : 1 

 and G : 3 ; this being made up of two 

 simple ones is called a Duplicate Ratio. 

 When three simple ratios are compounded, 

 they form a Triplicate Ratio ; if four, a 

 Quadruplicate Ratio, and so of other com- 

 pounds. 



RAY is a single radiation from a body which 

 sends out emissions in all directions. 

 See Radiation and Light. 



RAYS, ABERRATION OF. See Aber- 

 ration. 



KAYS, CALORIFIC. See Calorific Rays. 



COLOURED. See Colour* and 



Prismatic Spectrum. 



CONVERGENT. See Reflexion, 



Laws of. 



DIVERGENT. See Reflexion, 



Laws of. 



PARALLEL. See Reflexion, 



Laws of. 



REFLEXION OF. See Reflexion. 



REFRACTION OF. See Re- 

 fraction. 



ORDINARY AND EXTRAORDI- 

 NARY. See Refraction, Double. 



RE- ACTION. See Action. 



REFLEXION. See Gloss. I. 



REFLECTING Microscopes, &c. See 

 Gloss. I. 



REFRACTION. See Gloss. I. 



DOUBLE. See Gloss. I. 



REFRACTING Microscopes, &c. See 

 Gloss. I. 



REFRANGIBILITY. See Gloss. I. 



RELATIVE GRAVITY. See Gravity. 



REPULSION. See Gloss. I. 



RESINOUS ELECTRICITY. See Elec- 

 tric Fluid. 



RESISTING FORCE. See Force. 



RESOLUTION OF FORCES. See 

 Forces. 



RESULTANT. See Force*, Composition of. 



RHOMBUS. See Gloss. I. 



RIGIDITY. See Gloss. I. 



ROCHELLE SALT. See Gloss. I. 



RUBBER See Electricity. 



RUBY. See Corundum. 



RUPERT'S DROPS (so called because 

 they were first brought to England by 

 Prince Rupert, a German prince, and 

 grandson of James I.) are a sort of glass 

 drops with long and slender tails. They 

 will bear a smart stroke of a hammer, but 

 burst into atoms with a loud report if the 

 surface be scratched, or the tip of the tail 

 broken off. They are made by dropping 

 melted glass into cold water, which con- 

 denses the outer surface, and imprisons 

 the heated particles while in a state of 

 repulsion. See Annealing of Glass. 



SAFETY-VALVE (a necessary appendage 

 to a steam-engine) is a valve opening 

 outwards from a boiler, and loaded with 

 a weight sufficient to withstand the pres- 

 sure of the steam until it rise to a certain 

 required height ; but which would be 

 forced open before the steam could burst 

 the boiler. 



SAPPHIRE. See Corundum. 



SATURATED SOLUTION.-See Solution. 



SATURATION. See Electricity. 



SCALE. See Gloss I. 



SCREW See Gloss. I. 



SECTOR. A sector is any portion of a 

 circle (less than a semicircle) contained 

 between two radii and a part of the cir- 

 cumference : such as the triangular spaces 

 A C B and A C D, the former of which is 

 an acute-angled, and the latter an obtuse- 



