Sect. I. Of the SOLAR SYSTEM.

'rom the Sun; so is the Distance of the’lanet’s Orbit from the Earth’s in knownMeasure, to the Distance of the said Planetrom the Sun in the same Measure: Whicheing known, the Distance of all the other’lanets from the Sun may be found. For,t will be, as the relative Distance of anylanet from the Sun, is to its Distance fromim in a known Measure; so is the relativeistance of any other Planet from him, tots Distance in the same Measure. Thisay be done, by finding the Distance of thelanet Mars, when he is in Opposition to* Ithe Sun, after the same Manner as we find5 the Distance of a Tree, or the like, by two1 stations.

e Let <f be Mars, D the Point on the" ! Earth’s Superficies, where Mars is vertical,s when he is in Opposition to the Sun (whichnay be exactly enough found by Calculation)it which Time let an Observer, at the Pointr Z, (whose Situation from D must be known)ake the Altitude of Mars , whose Compo-nent will be the Angle <f ZR; then in thee Triangle cf Z C will be given the AnglecsZC, the Angle C (whose Measure is thef ^rch DZ) and consequently the AngleS £ <f C the Parallax, and also the Side Z C:he Semidiameter of the Earth; by whiche may find C cf the Distance of Mars fromhe Earth. The extreme Nicety requiredn this Observation, makes it very difficultC 3 to

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