KNOWLEDGE. 



October, 1912. 



Frost in their pajier " On the X'elocity of the Sun's 

 Motion through Space as Derived from the Radial 

 Wlocity of Orion Stars."* Professor Boss con- 

 tributed the further fact that their proper motions 

 are also ver)- small. Now. .\Ir. Benjamin Boss finds 

 that several groups of Orion stars are moving in 

 directions ven,- little removed from position-angles 

 which are 180" from the solar ape.x.* The proper 

 motions for one hundred and si.xtv-two of these 

 objects cluster around a mean value of 0"-0376. 

 The appap'nt solar parallactic motion for the same 

 areas (deduced from the entire body of stars included 

 in the research of Professor Lewis Boss) is 0"- 0349. 

 Hence the motions in question are almost entirely 

 j)arallactic. Here we have the very thing for which 

 Dr. Crommelin asks, namely, a body of stars of 

 galactic association (the mean galactic latitudes 

 averaging +11° and — 12° on either side of the 

 medial galactic circle), and one which reflects the 

 solar motion. Moreover, this is the most convincing 

 testimony that has yet appeared that the apparent 

 solar motion is really solar. If the solar velocity 

 is really as great as four astronomical units per 

 annum, these stars and the associated Milky Way 

 are 5 ■ 7 times as far away as the sixty light-years 

 assumed. Further investigations, allowing for 

 independent star-drift, may alter the value ascribed 

 to the solar velocity, but the general order of the 

 distances cannot be greatly changed. 



Kapteyn and Frost (Op. cit.) find from sixty-one 

 Orion stars having a mean cross-motion of 0"- 01 23 

 per annum, a radial velocity, freed from the parallac- 

 tic velocity, of 6-3 kilometres per second, which 

 corresponds to a parallax of 0"- 00924, representing 

 5-4 times the galactic distance of my preliminarv 

 assumption. 



There is an indication that the Orion-type stars are 

 moving along two distinct galactic streams which 

 have a trend oblique to the solar motion and away 

 from some common centre, the radial drift for these 

 stars near the solar apex being, in a general way, 

 similar in direction to that of the Sun's motion, 

 though less in amount, while on the opposite side of 

 the heavens the radial drift is opposed to the Sun's 

 motion. The result is that there is a difference of 

 ten kilometres per second in the solar velocity derived 

 from Orion stars near the apex and from Orion stars 

 near the anta[)ex. This conclusion is confirmed bcjth 

 by the measures of Kapteyn and Frost, and by those 

 of Stroobant on Orion stars. 



In view of the evidence which is presented here, 

 it appears to me probable that mv preliminary value 

 of the galactic dimensions may need to be multiplied 

 by five. The estimates of the nebular distances 

 must also be increased in the same proportion, 

 although it will, of course, be understood that, as this 

 problem lies on the utmost verge of possible solution, 

 any answer to it must be taken with considerable 

 latitude. 



[Supplementary Note. — Since writing the 

 above, I have seen the article by Dr. Max Wclf in 

 Astronomische Xachricliteii, No. 4549, in which he 

 also arrives at the conclusion that my earlier esti- 

 mates of nebular distances and dimensions should 

 be increased about five-fold, but basing his argument 

 on the supposition that the parallax of Nova Persei 

 is 0"- 01, instead of 0"-05. This value seems inad- 

 missible for the reasons cited here. The hypothesis 

 that the Galaxy is a spiral w ith two branches and 

 more than one turn, and that the Nova was on an 

 adjacent branch, will remove this remaining dis- 

 crepancy.] 



■'■'■ Astrophysical Journal. Vol. XXXII. page 83, July. 1910. 

 ■ Systematic Proper-motions of Stars of Type B." Astronomical Journal. No. 620, page 163. December 5th, 1910. 



EXTENSKJX LPXTL'RES. 



We have pleasure in mentioning the work of the 

 Extension Section of the Manchester Microscopical 

 Society, which each year sends out a list of lectures 

 of a popular character which can be given before 

 societies in and about Manchester, the cost as a rule 

 being limited to the expenses, as the work of lectur- 

 ing and demonstrating is entirely voluntan,- and 

 gratuitous on the part of the members. It is obvious, 

 as a rule, that only a few shillings will be asked for 

 from the societies which take advantage of the help 

 which is offered. Occasionally a small fee is 

 demanded, and this is the case where lectures are 

 given before societies which are commercial under- 

 takings, or are subsidised out of Government or 

 public grants. The fifteenth list is before us for 

 the session 1912-1913, and on it are si.xty-eight 

 subjects and the names of seventeen lecturers. \\'e 

 quote one or two of the titles : — " Some of Life's 

 Simplest Children," "The Natural Histor\- of 

 Lizards," "A Study of the Fertilisation of Flowers," 

 " Household Pests," " Prehistoric Man," " The 



Management of an .Aquarium." It will be seen that 

 they are mostly natural histor\- subjects, and 

 secretaries of societies within reach of Manchester, 

 will receive a copy of the list on application to Mr. 

 R. Howarth, the Honorar\- Secretar\- and Treasurer, 

 90, George Street, Cheetham Hill, Manchester. 



It would be a ven,- good thing if other Societies 

 were to follow in the footsteps of the Manchester 

 Microscopical Society. The Council of the 

 Selborne Society, we know, has arranged series of 

 local lectures quite apart from its branches, and 

 several of its members have given addresses to 

 some of the local societies which are not able 

 to pav large fees. The South- Eastern L'nion 

 of Scientific Societies has for many years published 

 lists of their members who are lecturers, with 

 a selection of their subjects. This work, how- 

 ever, might be very well extended and systema- 

 tised, and we should be glad to hear from any 

 of our readers in any district who are willing 

 to give lectures if their expenses are paid. 



