194 ASTEONOMY. 



his observations, and the resulting parallax, 8". 79, indicates that val- 

 uable results may be obtained by this method by small instruments. 



Observations of the declination of Mars made in 1877 at Leyden and 

 Melbourne have been used by Mr. Downing to find a value for the solar 

 parallax. The result is 8".9G (A. K 22SS). It is remarkable how well 

 this agrees with Stone's and Winnecke's results from the oi^position 

 of 18G2 (8".93 and 8".96). 



Vol. 1, part 3, of the "Astronomical Papers prepared for the use of 

 the American Ephemeris and Nautical Almanac," containing the experi- 

 ments upon the velocity of light, made by Master A. A. Michelson, 

 U. S. N., has just been i)ublished. His method of investigation (an im- 

 proved form of Fouoault's method) is described in the section on 

 " Physics." 



The final value for the velocity of light in vacuo is 299,944 ± 51 (in 

 air, 299,804), or, in round numbers, 299,940 kilometers per secoud = 

 180,380 miles per second, the remarkably small error, ± 51 kilometers, 

 being composed of the total constant error in the most unfavorable case, 

 and the probable errors of observation. This quantity, i 51 kilometers, 

 cannot be said to express the probable error of the determination, in the 

 ordinary acceptance of the term ; combining, as it does, accidental errors, 

 strictly speaking, and estimated constant errors. 



These experiments were made by Master Michelson at the Xaval 

 Academy, Annapolis, at private expense, and to him the entire credit 

 is due. A new determination of the velocity of light, embodying es- 

 sentially the same arrangement, but with more elaborate and expensive 

 apparatus, has been completed by Professor Newcomb, superintendent 

 of the Nautical Almanac ; and this combined with a revised constant 

 of aberration, will give the best value of the Solar Parallax. 



Transit of Ve7ius December 6, 1882. — The Astronomer Eoyal has pointed 

 out the best stations to be occupied for observations of the next Transit 

 of Venus. 



Ingress accelerated can be well observed in Cape Colony, Africa. Mr. 

 Gill, will soon determine his longitude telegraphically. 



Ingress retarded should be observed in the West Indies. These longi- 

 tudes have been determined already by officers of the United States 

 Navy. 



Egress accelerated may be observed at the West India stations and 

 along the east coast of the United States. 



Egress retarded : Stations in New Zealand are best suited, although 

 Australian stations will serve. 



SOLAR eclipses. 



Professor Newcomb has published a paiier " On the recurrence of 

 Solar Eclipses, with Tables of Eclipses from b. c, 700 to A. D. 2300" 



