8 ANNIVERSARY ADDRESS. 
I. Trigonometrical, such as the transit of Venus; II. Grave 
tational, such as that by Le Verrier, who obtained the mass 
of the earth from its effect upon Venus and Mars; III. The 
phototachymetrical, that is, by the measurement of the velocity of _ 
light; and he has collected together a great number of the determi- 
nations which have been made. After a most elaborate discussion 
of these, he gives the following tabular statement, which shows — 
the probable limits of the value of the parallax according to — 
each method :—I. Trigonometrical: Meridian observations of 
Mars 8°84”_8-96"; diurnal observations of Mars, 7.¢., observing 8 
it rises and sets, 8-60’-8-79"; asteroids, 8°76’—8-88" ; transit 
of Venus, 1769, 8°55’-8-91"; transit of Venus, 1874, 8-76-8980"; 
_ UL. Gravitational methods : By the mass of the earth, 8°80"-8-94"; 
parallactic inequality, 8-78”—8-91” 3 lunar inequality, 8-66’-9:07". 
Tit, Phototachymetrical : Velocity of light and equation, 872’- 
8°89" ; velocity and aberration, 8-73’-8-90”. In addition to these | 
we have the value derived from the American transit of Venus 
photos. in 1874, which is 8-883; but no value derived from the 
American contact observations has yet been published. We have 
also the results of the meridian observations of Mars in 1877, 
published by Professor Eastman, combining—Washington and 
Melbourne gives 8-971”; Washington and Sydney, 8°885"; Wash 
ington and Cape of Good Hope, 8-896”, I may mention here, that 
the Sydney observations of Mars, used in the above determination, ; 
were the first important ones made with the new transit instr ; 
ment; and it is satisfactory to see that they givea value of the 
parallax nearer to the probable value than the others. As to the 
value of the parallax, you will see that the range is from 8°55h. #0 
9:07, i.¢., from 90 to 95} millions of miles, Mr, Harkness says'~ 
“We only know that the parallax seems to lie between 8°75" aes 
890" and is probably about 8-85”, Now, 8-846” (92,400,000 miles) | 
is the final value of the parallax derived from the English and 4q 
Australian observations by Captain Tupman and accepted by St 
George Airy. 7 
Reference has already been made to the International Confer 
ence of Astronomers which was hela in Paris, in October, 188 
