ASTRONOMICAL OBSERVATIONS. 51 



Pennfylvania avenue between the capitol and Prefident's 1 

 Hcuie, and Maryland avenue weft of the capitol n:al;e an > 70" 30' 23' 

 angle with the meridian of - - J 



All the lines of the city in which I have been concerned 

 were traced widi the fame inftrument wliicli I ufeJ on the lined 

 of the ten miles fqiaare, bat as the northern part was not finifli- 

 ed when I left tliat place, I cannot pretend to fay what method 

 has been fmce purfued. 



This paper being already carried to a greater length than I 

 at firft intended, (but upon looking over my notes I find it is 

 yet flrort of what was originally defigned for the fociety,) I 

 mult therefore in confequence of numerous avocations, referve 

 the remainder for a future communication, and proceed to the 

 fubjefts of aberration and nutation. 



N°. VIL 



Of the Aberraiion of the Stars, Nutation of the Earth^s Axis, 

 and Semiannual Equation, by Andrew Ellicott. 



PART SECOND. 



Of the Aberration of the Stars. 



Read Apru'^ | HE aberration of the ftars is their fmall apparent 

 3, 1795- X motion occafioned by the velocity of the Earth 

 in its orbit bearing a fenfible proportion to the velocity of 

 light. To give an idea of this effecT:, fuppofe an infinite number 

 of particles of matter moving in the direftion of A towards B 

 (Fig. I Plate I.) at the fame time fuppofe the tube a to be 

 moving towards C and preferving its parallelifm ; then if the 

 velocity of the tube a towards C bears no fenfible proportion 

 to the velocity of the particles moving from A towards B, a 

 particle which enters the centre of the tube at top will fall 

 upon the centre at the bottom. But if the velocity of the tube 

 towards C bears a fenfible proportion to the velocity of the 

 particles moving from A tov/ards B, then the particles w-hich fall 



into 



