244 KANSAS CITY REVIEW OF SCIENCE. 



It may be asked, since we know the distance of the sun, why send expedi- 

 tions to observe the coming transit. The answer is the precise parallax is not 

 known, it being still uncertain within a few hundredths of a second. We do rot 

 know whether it is 8.79, 8.8 or 8.8t seconds. The rays of the Sun heat the at- 

 mosphere of the enrth and produce a tremulous motion in the focus of a tele- 

 scope just where the micrometer is, and another trouble is that Venus has an at- 

 mosphere which refracts a ray of light somewhat rendering uncertain the exact 

 instant of contact with the solar limb. And it is to determine these corrections 

 to the last transit, and also to verify the measures of 1874 with improved instru- 

 ments that so much time, labor and skill are to be expended. And there is also^ 

 a higher aim than this, and that is to leave to future astronomers who will behold 

 the next transit, June 8, ^5004, all the data possible for the mathematically exact 

 determination of the great problem. 



One method of observing the transit is to photograph Venus while on the 

 Sun and then make computation at leisure; a method radically different from that 

 of measuring directly with a micrometer at the time of transit. 



A brisk controversy is now being held by astronomers as to which plan has- 

 the least objections, the apparent majority as the case now stands being opposed lo- 

 photography. The British photographic results were conflicting in 1874, the de- 

 ductions being, Airy 8.79, Tupman 8.81 and Stone 8.88. Other values deduced 

 by direct measures range from 8.78 to 8 84 seconds. From a careful comp rison 

 of all available records of the problem the writer is convinced that' the parallax of 

 the Sun is 8.8 seconds. 



There are a number of ways of determining this constant in nature withtjut 

 resorting to transits of Venus, the most important being based on the velocity of 

 light and the law of gravity. And these confirm the best results of transits in 

 placing the parallax at 8.8. 



This is the most valuable number known to man, since it enables him to 

 measure the distances, diameters, volumes, weights and densities of all bodies in- 

 the solar system ; and when he has weighed all these, to soar away into the in- 

 finitude of space and weigh other suns than ours and tell their distances. 



In conclusion we will endeavor to show with what refinement measurement 

 is expected to be made next December. 



Thus: by taking the parallax to be 8.8 seconds, the distance of the Sun be- 

 comes 92,882,917 miles. Now if we assume it to be 8.81 then the Sun's distance 

 will be 92,777,488 miles or 105,429 miles nearer, that is a hundredth of a second 

 of parallax equals 105,429 miles in the length of a line reaching from the earth to 

 the Sun. But the hundredth of a second is the equivalent to the angle. subtended 

 by the diameter of a hair placed at a distance of 800 feet. Young, The Sun, 

 p. 23. 



The observers must have micrometers delicate enough to measure these excess- 

 ively minute distances with precision, or we shall not derive benefit from the 

 transit. However, the Clarks with their elegant telescopes and micrometers will 

 prove equal to the occasion. Such precision would not be necessary were it not 



