196 



KNOWLEDGE. 



May, 1913. 



either in revealing planetary detail, or in separating 

 close double stars. But the attempt has been 

 defeated, both by theory and observation ; 

 (a) by theory, because of the law of diffraction, 

 which proves that the defining power of a 

 telescope increases with its aperture ; and (b) by 

 observation, from the evidence of the facts them- 

 selves. A comparison of the appearance of Syrtis 

 Major on Mars with various instruments in 1909, 

 when the weaker telescopes revealed inexistent lines 

 while failing to show the coarsest details (see 

 Figures 190 to 193) will establish for ever their hope- 

 less inferiority. Nor was the smaller instrument 

 more fortunate on double stars. A spurious 

 satellite to Sirius was discovered and measured in an 

 impossible position in 1896, with a refractor of 

 moderate power. But when the question of finding 

 the true satellite was seriously raised, the discovery 

 was naturally made with the thirty-six inch 



equatorial of the Lick Observatory, one of the most 

 powerful instruments in existence. 



Thus it is that diffraction fetters the efficiency of 

 small telescopes ; and their comparison with large 

 ones is as childish as the attempt to bombard a fortress 

 twenty miles off with guns whose range is only eight. 



Such the errors foisted on the scientific world, and 

 such the arguments leading to their final refutation. 

 Yet truth will seldom receive acceptance without 

 strenuous opposition. The laws of perspective will 

 again be curbed by the evidence of lines appearing 

 straight in all positions of a rotating globe. Some 

 observers will continue proclaiming the superiority of 

 small telescopes. Ponderous volumes will still be 

 written to record the discover}- of new canals. But 

 the astronomer of the future will sneer at these 

 wonders ; and the canal fallacy, after retarding 

 progress for a third of a century, is doomed to be 

 relegated into the myths of the past. 



STONYHURST COLLEGE OBSERVATORY. 



By FRANK C. DENNETT. 



The report of this useful observatory for the year 1912 has 

 just been issued by its Director, the Rev. Walter Sidgreaves, S.J ., 

 F.R.A.S. The mean barometric pressure for the year was -054 



Tablk 39. 



Magnetic mean declination range. 



Mean daily spot area. 



inch below the average of the previous sixty-five years, and so 

 lower than 1911. Only in the months of April, September, 

 October and November was it above the month's average ; 

 September yielding the highest mean, and March the lowest 

 of the year. The rainfall was nearly seven and a quarter inches 

 above the annual average, for which the excessive rains in 

 March, June, August and November were largely responsible. 

 During March the fall was half an inch above double the 

 usual fall, being 7-205 inches, the greatest during the previous 

 sixty-five years. April proved the finest month, the only one 



with the duration of sunshine above its average, and its rain- 

 fall little more than half its average. The total duration of 

 sunshine during the year was only 927-6 hours, or 409-6 

 hours short of the annual average, the smallest on record for 

 thirty-two years. The dullest months, March, June, August, 

 and December all yield the lowest number of shining hours 

 previously on record. The year, notwithstanding the small 

 amount of sunshine, proved a mild one, for though the 

 summer was below the average, the winter was above. The 

 mean temperature for the year was 47° -5, or :> -6 above the 

 average. Only on five days the wind attained the velocity of 

 a gale, the strongest being on April 6th and 8th, when the 

 record stood at forty-five and forty-six miles per hour. 

 Magnetic records appear to be missing on three days, 

 September 30th, November 18th and 19th. Of the rest, 

 one hundred and twenty-four days are recorded as calm, two 

 hundred and twenty small disturbance, eighteen moderate, 

 and only one, October 14th, as great, no very great dis- 

 turbances being recorded. The mean daily range of the 

 Declination magnet in arc minutes was 8'-l, the lowest of the 

 past eighteen years. The lowest monthly mean daily range, 

 6'-l, was in January. The mean area of sunspots (in units 

 of irnireth of the visible surface) appears at 0-22. Compared 

 with previous years, together with the magnetic declination 

 range in graphical form, it seems to show that 1912 marks the 

 minimum of sunspot activity. The diagram is constructed by 

 the writer from the Stonyhurst records since 1898, and is 

 perhaps more striking than figures. The spectrum of Nova 2 

 Geminorum was photographed on seven occasions, besides 

 being observed visually on other nights. Gale's and Borelli's 

 comets were both photographed and observed, but not under 

 favourable conditions. 



One sentence in the report we note: ' It has been decided 

 at the Meteorological Office to reduce the number of its 

 observing stations ; and our connection with the office ceases 

 at the end of March. But the automatic recorders are to 

 remain here, and will be kept in active service." 



