IOWA ACADEMY OF SCIENCES. 75 



equatorially mounted, b}^ Brashear, was employed, using 

 a Herschelian diagonal eye-piece with various powers, 

 usually one magnifying about 78. The method of projec- 

 tion of the solar image to a diameter of 8 or 10 inches was 

 sometimes used, and the positions of the spots and faculae 

 determined by means of Thomson's discs; but generally 

 the relative heliographic positions were noted by means of 

 cross wires in the eye-piece, and afterwards reduced by 

 reference to the usual "tables for physical observations of 

 the sun/' 



A spectroscope with a 2- inch Rowland diifraction grat- 

 ing of 14,438 lines per inch, was employed in viewing tlie 

 prominences and examining spot spectra. 



Daily observations were taken, usually about noon in 

 the autumn and winter months, and in the morning 

 between 7 and 8 o'clock during the warmer seasons, when 

 better definition was secured than during the hotter por- 

 tion of the day; the visual observations consisted of noting 

 the number of groups of spots — each disturbance of one or 

 more spots being considered as a group — the total number 

 of individual spots in each group, and the number of 

 groups of faculae. The relative positions of each of these 

 were plotted on paper, and a sketch made of the appear- 

 ance of each group, with more detailed drawings of the 

 greater disturbances; in addition, the condition of the defi- 

 nition was noted with reference to the visibility of the 

 granulation of the solar surface and lastly the time of the 

 observation was inserted. The daily results thus obtained 

 have been published from time to time in various journals, 

 and for reference a list is appended to this paper. 



During the period under review, about 1,750 groups have 

 been observed on the visible disc, the greatest number, 

 285 being registered in the year 1893, and least number, 

 eighteen, in 1901. 



As the purpose of this paper is but a review of the recent 

 solar cycle of sun-spots, a detailed account of the observa- 

 tions is not attempted, reference for these being made to 

 daily results as contributed to journals and societies given 

 in the list appended, as before mentioned; hence only the 



