THE STARRY HEAVENS IN NOVEMBER 



235 



trouble. He will see the brilliant cres- 

 cent increasing rapidly in size but also 

 growing narrower. It is at this time, 

 too, that the crescent can be clearly 

 seen to exceed a half circle in length, 

 a fact which clearly proves that Venus 

 is surrounded by a heavy atmosphere. 

 Mars sets in the southwest less than 

 one hour after sunset on Nov. 1, and 

 this time decreases to only twenty min- 

 utes by November 20. The planet will 

 not enter the morning sky however un- 

 til December 24th. 



Jupiter and Saturn are both in excel- 

 lent position for observation, the 

 former in the southeastern, and the 

 latter in the northeaster n, sky. 

 Throughout the month Saturn will re- 

 main near the bright star at F, Figure 

 1, and it will be easily possible, by 

 carefully comparing the relative posi- 

 tion of these two objects from time to 

 time, to detect the motion among the 

 stars of this very slowly moving world. 

 Uranus is in Capricornus, a little to 

 the right of Jupiter, and Neptune is in 

 Gemini, beyond the borders of our 

 evening map. 



The interesting bright comet which 

 has been easilv visible to the eve in 

 the north will, during November, fol- 

 low the path AB, Figure 2. During this 

 time its distance from the earth will 

 increase from one and sixty-one to 

 one hundred and eighty-five millions 

 of miles and it will consequently lose 

 one-third of its brightness. It will, 

 however, remain a bright and interest- 

 ing object in a small telescope. 



There are no less than three other 

 comets now in the sky, but these are 

 far fainter and can only be viewed in 

 a large telescope. 



The Transit of Mercury. 



This most interesting phenomenon 

 will occur on the morning of Nov. 7. 

 The small, round, intensely black disc 

 of the planet will enter upon the sun's 

 disc at 4 hours 57 minutes A. M. and 

 will leave it at 9 hours 10 minutes 

 A. M. (Eastern Standard Time), the 

 entire transit thus occupying four 

 hours and thirteen minutes. As the 

 sun does not rise in the eastern states 

 until 6 hours 36 minutes A. M., from 

 this region it will be seen to emerge 

 from below the ground with the planet 

 already advanced one-third of the way 

 upon its disc. To observers west of the 

 line A. B., Figure 3, the sun will not 



rise until the transit is over, so that 

 to them the phenomenon will be 

 \vh< illy invisible. 



Such transits afford valuable data for 

 improving our knowledge of the path 

 and motion of Mercury; it has also 

 been shown from an elaborate study of 

 all of them that the length of our day, 

 — the unit of all time— is, as nearly as 

 we can determine it, invariable. It is 

 also when Mercury is in transit that 

 evidence of its possessing an atmos- 

 phere is searched for. 



The next transit of Mercury, after 

 this one, will not occur until the even- 

 ing of May 7, 1924. This will not be 

 visible from the eastern parts of the 

 United States. 



Feeding Habits of Fresh Water 

 Mussels. 



The Biological Bulletin for Septem- 

 ber prints some new observations on 

 the feeding habits of eight different 

 species of American fresh water mus- 

 sels. 



The food is largely microscopic 

 diatoms and desmids with less amounts 

 of animalculae, minute eggs, and the 

 free-swimming spores of green plants. 

 These come in with the water for res- 

 piration which is drawn through the 

 syphon at the rate of a little less than 

 three pints an hour for a seven ounce 

 animal. The cilia which everywhere 

 line the gill chambers, whip these 

 small particles toward the mouth, 

 while a coating of mucus gradually 

 unites them into convenient lumps. 

 Non-edible particles are agglutinated 

 in the same way, and then expelled by 

 a sudden current made by closing the 

 shell. 



All the foodstuff that happens to 

 come in the water is swallowed 

 whether the animal is hungry or not; 

 but only so much is digested as the 

 creature happens to need. 



They are trying at the University 

 of Pennsylvania a new method of get- 

 ting cultures of amoeba. Instead of 

 the customary hay infusion, they are 

 mixing samples of water taken from 

 many different sources — clear and stag- 

 nant ponds, swamps, sewage-polluted 

 streams, ditches, and the like. In this 

 manner, they make sure of getting a 

 mixed culture which contains both the 

 amoeba and its food in a sort of "bal- 

 anced aquarium." 



