Spsyey ” 7F | he 
XXII. On rhe Periods of the Changes of Light in the Star 
Algol. Ina Letter from John Goodricke, E/g. to the Rev. 
Anthony Shepherd, D. D. FR. S. ii effor %, Aftronomy ak 
_ Cambridge. 
Read Aprilr, 1784. 
ST R,. York, Dec: 8, 178%. 
S Iam now able, by collating fome of my late obferva— 
. tionsen Algol with thofe I fent you laft May, to deter-: 
mine with greater precifion the periodical return of its changes,. 
1 wifh to add this as a kind of fupplement to that account. 
The method I have here purfued is by taking the intervals 
between. accurate obfervations of Algol’s leaft brightnefs or 
greateft diminution of light made at long diftances of time 
from-each other, and dividing thofe intervals by a certain num-. 
ber of revolutions, as will be beft underftood by the table be- 
low. The reafon of my chufing: long intervals is, that the 
number of revolutions being greater, the errors of obfervatiom 
are’ thereby diminifhed:: all error cannot,. however, as yet be: 
excluded, but I think the period is now, by the following. alt 
cols pe tined within ten or fifteen. feconds. 
2 Mean 
