252 



KNOWLEDGE, 



[November 1, 1898. 



the other of the place it would have as seen from the 

 centre of the earth. This shift gives the means of 

 deducing the planet's distance from the earth in miles, 

 and the distance of the sun then follows from Kepler's 

 laws. Now, a minor planet, which looks like a stellar 

 point in the telescope, can be measured with much greater 

 precision than can a large, bright, unequally illuminated 

 disc like that of Mars. Dr. Gill's recent determination of 

 the sun's distance (ninety-two million, eight hundred and 

 seventy-four thousand miles), which is probably the most 

 accurate yet made, was based on heliometer observations 

 of Iris, Victoria, and Sappho, whose least distances from the 

 earth (in astronomical units) are 0-81, 0'8'2, and 0H4 

 respectively. It will be seen at once what an improvement 

 will be effected when DQ is observed at a distance of 0'14, 

 or only one-sixth of that of the above three planets. lu 

 fact, any uncertainty in the sun's distance will be reduced 

 to one-sixth of its present amount. Even the approach in 

 the autumn of 1900, though far from being the most 

 favourable possible, should certainly be utilized for 

 heliometer measures, for its distance will be little more 

 than one-third of that of the three planets measured by 

 Dr. GiU. 



Another way in which DQ will assist in improving our 

 knowledge of the sun's distance is by the perturbations 

 which the earth produces on it, which will be very con- 

 siderable, and which will give an accurate determination 

 of the earth's mass compared with the sun's, and hence of 

 the latter's distance. But this method will not be avail- 

 able for many years ; it will, however, in the long run, 

 give very accurate results. 



It might at first sight appear that DQ will make still 

 closer approaches to Mars than it does to the earth, but 

 this is not the case ; owing to the fact that the orbits are 

 so much inclined to one another, and the unfavourable 

 position of the line where their planes intersect one another 

 (in longitudes 115'' and 295"), they do not approach more 

 nearly than 0-23 in astronomical units. 



As viewed from Mars the motion of DQ would be very 

 singular, for sometimes Mars would overtake DQ, some- 

 times it would be overtaken by it, sometimes DQ would be 

 in inferior conjimction with the sim, sometimes in opposi- 

 tion to it, sometimes in Mars' equator, sometimes at his 

 poles. 



As viewed from the earth there is one feature in which 

 DQ differs from all the other superior planets ; they are in all 

 cases retrograding when in opposition, but DQ when in 

 perihelion has a velocity whose resolved part in the plane 

 of the ecliptic is 18-95 miles per second, while that of the 

 earth in the same longitude is only 18'78 miles per second. 

 DQ is therefore gaining on the earth instead of being left 

 behind, and it will therefore be slowly advancing in longi- 

 tude ; it will have a rapid southward motion in latitude in 

 consequence of its high inclination which will amount to 

 about 1^^ per day. When in opposition near aphelion it 

 will retrograde in longitude i° per day as was the case at 

 its discovery ; there will necessarily be an intermediate 

 position where it will be exactly stationary in longitude 

 at the instant of opposition, and the earth and planet will 

 travel on side by side with the same velocity, maintaining 

 for some days an almost constant distance. 



It has been suggested that DQ may have only recently 

 been introduced into its present orbit by perturbations, but 

 this does not seem to me to be possible if its minimum 

 distance from the earth be 0'14, for the perturbations by 

 the earth at this distance though considerable, would not 

 be able to change the orbit ;)<■»• saltum, and the giant planet 

 Jupiter, the great disturber of the minor planets, never 

 approaches DQ more nearly than 3-2, at which distance 



it would likewise be unable to effect any sudden great 

 change in the orbit. 



Many of the relations I have referred to above are 

 illustrated in the diagram. To picture the orbits of DQ 

 and Mars correctly, we must imagine them rotated about 

 their lines of nodes through anj^des of eleven degrees and 

 two degrees respectively. In the case of DQ the upper 

 left hand portion of the orbit will be the highest above the 

 plane of the paper, in the case of Mars the lower left hand 

 portion. 



I have now dealt with the relations of the new planet to 

 ourselves as fully as our present knowledge of its orbit 

 appears to warrant. A more accurate computation, based 

 on a larger series of observations, will be awaited with 

 keen curiosity ; after which its past and future history 

 may be traced with a closer approach to precision than is 

 possible at present. 



^— ♦- 



THE NOVEMBER METEORS. 



PROF. E. C. PICKERING, in Circular No. 31 of the 

 Harvard College Observatory, points out that it 

 is very important that a continuous watch should 

 be kept during the two or three days in which the 

 Earth is passing through the denser portion of 

 the meteor stream. This can only be done by establishing 

 a series of stations in various longitudes, so that during the 

 entire time one or more of these stations shall fulfil the 

 conditions that the radiant point shall be above the horizon 

 and the sun below. The watch should be begun on the 

 evening of November 11th, and continued each night 

 until the shower is clearly past. Prof. Pickering recom- 

 mends all observers to note the following particulars : — 



Name of observer, location of station, post office 

 address, time of beginning and ending of observations, 



The Constellation Leo with Stellar Standards of Beferencc. 



interruptions by clouds or other causes, condition of eky, 

 as clear, hazy, passing clouds, itc. He then adds the 

 following directions: — 



" The observations most desired are those required to 

 determine the frequency of the meteors. They are of 



