August 1, 1890.] 



KNOWLEDGE. 



187 



will never be less than 1| seconds, so that this fine pair 

 will always remain within the range of moderate sized 

 telescopes. My elements, combined with Kriiger's parallax 

 of 0'1G2", give the sum of the masses = 2-777 times 

 the mass of the sun, and the mean distance between 

 the components 27'777 times the sun's distance from the 

 earth. 1 find that the plane of the orbit is at right angles 

 to the phme of the Milky Way. 



15. Stnnr 228. — I have recently computed an orbit for 

 this pair which represents all the measures from 1829 to 

 1889, fairly well for so close a star. Fig. 9 represents the 

 (ijilifiiriit ellipse I have found. According to this orbit 

 the distance between the components, which is at present 

 about 0'4", will gradually increase during the next few 

 years up to 0'.55", then iliminish again as the companion 



Sca/^ p/ ,>■«. 



Fic. 11. — -Ari'ARF.NT Orbit of 83 Peg\si. 



approaches the periastron. The minimum distance will 

 not be reached till the position angle is nearly 180^ (after 

 the periastron passage), when the components will probably 

 be separated by less than 2". 



IG. y Coriiiur lloiralis. — For this close and difficult 

 double star Dr. Doberck finds a period of 95| years. As 

 in the case of 42 Couue, the plane of the orbit nearly 

 passes through the earth, and the apparent orbit is nearly 

 a straight line. For the past ten or eleven years this star 

 has been " single," even with the largest telescopes. I 

 find that the plane of the orbit is at right angles to the 

 plane of the Milky Way. An orbit has recently been com- 

 puted by Celoria with a period of 85-270 years. 



17. ^ Sturpii. — A remarkable triple star; magnitudes 

 about 4s, 5, and 7i. The companion of the close pair has 

 described a complete revolution since its discovery by Sir 

 W. Herschel in 1780. Dr. Doberck finds a period of 

 95-9 years. The real orbit is nearly circular, but owing 

 to its high inclination —about 70° — the ((ji/iiiiidI orhii is 

 a very elongated ellipse, as shown in Fig. 10. All three 

 stars have a common proper motion, and probably form 

 one system, but tiie motion of tlie third star is very slow. 



and its period of revolution must be several hundred 

 years. 



18. 85 Pci/ii.fi. — A well-known wide double star; 

 magnitudes about 6 and 9, and present distance about 

 22". In 1878 Burnham discovered the brighter star to 

 be a close and difficult double, and since that year the 

 companion, which is about the 11th magnitude, has de- 

 scribed no less than 220^ of its apparent orbit. Mr. 

 Schaeberle, of the Lick Observatory, has recently computed 

 an orbit, and finds a period of 22-8 years, with a high 

 inclination, which makes the apparent orbit, shown in 

 Fig. 11, a rather elongated ellipse. Assuming a parallax 

 of 0-054" found by Briinnow, I find the mass of the system 

 11-297 times the sun's mass, with a mean distance of 

 17-777 times the sun's distance from the earth, or a little 

 less than the distance of Uranus from the sun. As, how- 

 ever, the assigned parallax is so small, its accuracy is 

 somewhat doubtful. A parallax of 0-0",4" would imply a 

 distance of 3,819,722 times the smi's distance from the 

 earth, or about 60 years' journey for light. From the 

 recorded measures of the distant companion I have com- 

 puted the proper motion of the binary pair, and find it to 

 be 1-221" in the direction of position angle 141-25°. This 

 proper motion combined with the above parallax would 

 imply a real motion of about 66 mUes a second. 



HOUSE-FLIES AND BLUEBOTTLES.- 



By E. A. BuTLEE. 



-VI 



FLIEH are subject to the persecutions of animal as well 

 as vegetable parasites, some of which attack 

 them externally and some internally. The chief 

 external one is a reddish kind of mite (Fig. 16). 

 These creatures may be found, principally during 

 the summer months, on diS'erent parts of the bodies 

 of the flies, especially on the under surface ; here, 

 in the neighbourhood of the attachments of the legs, 

 and at the junctions of the body segments, there 

 are plenty of places — the 

 joints of the armour, as it 

 were — where the skin is thin 

 enough for the mites to pierce 

 with their snouts. They show 

 a good deal of enterprise in 

 endeavouring to secure the 

 best places — no easy matter 

 when there are a good number 

 of them — and when one has 

 plunged its proboscis into the 

 S) tlesh, it adheres most tena- 

 / ciously, and its body may be 

 lifted up and pushed from side 

 to side without causing it to 

 relax its hold. The tlies, 

 though so particular in re- 

 moving from their persons the 

 slightest trace of inanimate 

 foreign matter, by sweeping 

 and scraping themselves with 

 their legs, yet submit patiently 

 to the presence of their living 

 get into places whence they 

 could, one would imagine, easily be removed. For 

 example, a Mu.scn iluiiustiiii that has just at the moment of 

 writing alighted on the window pane, flew about uncon- 

 cernedly with a large mite clinging to its face in such a 

 way as one might suppose would have seriously interfered 

 with tiio use of iioth eves and antenuie. It did not seem, 



Fiii. K). — Mite Parasite on 

 Fi.v. Tiilcen from body of I'ol- 

 hnia riuii's 



burdens, even when they 



