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Y. 



ON THE LUNAR ECLIPSE OF JANUARY 28, 1888. By A. A. 

 RAMBAUT, M.A. 



[Read February 14, 1888.] 



Previous to tlie total lunar eclipse of October 4th, 1884, very little 

 attention was paid to such phenomena. Consequently eclipse 

 after eclipse was allowed to pass by without any unusual stir in 

 the observatories. There were, of course, accounts in the astro- 

 nomical Papers from a few observers, noting the colour of the 

 moon, and giving a general description of its appearance in the 

 various phases, but up till the year 1884, astronomers never made a 

 combined effort to utilise the occasion, because the phenomenon 

 did not appear capable of being turned to any practical use. 



On the occasion of the eclipse of October 4th, 1884, however, 

 it was proposed by Professor Otto Struve, of the Poulkova Observa- 

 tory, to employ the interval during which the moon was obscured 

 in observing occultations of a number of stars, with the object of 

 obtaining a more correct value of the moon's parallax and semi- 

 diameter. 



Although the method by which the moon's parallax is derived 

 from occultations of stars is necessarily of a complicated nature, it 

 will be seen from the following simple considerations that a number 

 of such observations, made at different stations on the globe, will 

 furnish data for its determination. 



If zs is the moon's equatorial horizontal parallax, and 



6 its hour angle at the moment of observation, 



8 its declination, and 



$ the latitude of the observatory, 



then the displacements in R. A. and decimation due to parallax 

 are given by the equations 



Aa = zj cos <p sin 0, and 



AS = ix [sin <p cos § + cos $ sin § cos 0], 



