178 REPORT— 1878. 



was regular (as in the case of the 13-sieve and 17-sieve, where the holes 

 slope down in parallel lines) the entry of the factors was much facilitated. 

 Great care was always required in order to be certain that no factor had 

 escaped entry ; but this examination was much more rapidly performed when 

 the pattern was fairly regular. The size of the volume would, however, be 

 increased very greatly if all the factors were given, without any propor- 

 tionate advantage. Burckhardt's arrangement of the table is an admirable 

 piece of condensation, p as the least factors of 9,000 numbers are given, in 

 the space of half a square foot, on each page. 



It will be evident from this description that it would be just as easy 

 to enter all prime factors in the table as to enter only the least ; and if all 

 the prime factors were entered the verification would be easier, and in the 

 numbers entered by the multiple method no error could occur, unless the 

 same mistake were made independently in entering both factors. 



The methods described in this section are no doubt practically iden- 

 tical with those employed by Burckhardt, and the calculation of the million 

 suggested no improvements upon them, except in a few matters of detail. 

 The construction of the table, though very simple in theory, required such 

 continual care at every step, and such constant supervision, that it could 

 not be undertaken by any one who was not prepared to devote a great 

 portion of his time to the work. • 



Eleventh Report of the Committee, consisting of Professor Everett, 

 Professor Sir William Thomson, Professor J. Clerk Maxwell, 

 Mr. G. J. Symons, Professor Ramsay, Professor Geikie, Mr. J. 

 Glaisher, Mr. Pengelly, Professor Edward Hull, Professor 

 Ansted, Dr. Clement Le Neve Foster, Professor A. S. Herschel, 

 Mr. G. A. Lebocr, Mr. A. B. Wynne, Mr. Galloway, and Mr. 

 Joseph Dickinson, appointed for the purpose of investigating the 

 Rate of Increase of Underground Temperature downwards in 

 various Localities of Dry Land and under Water. Drawn up 

 by Professor Everett {Secretary). 



Dr. Stapff has continued his observations of the temperature in the 

 St. Gothard Tunnel, and has contributed to the Swiss Natural History 

 Society a paper* of 56 quarto pages, embodying the results. 



The following is his description (pp. 26, 27) of the mode of observing 

 the temperature of the rocks in the tunnel : — 



" The exact determination of the temperature of the rocks in the tun- 

 nel formerly occasioned a notable expenditure of time and money. At 

 first thermometers about a metre long (made by J. Goldschmid, of Zurich) 

 were employed for this purpose ; their tubes being cemented into a wooden 

 cylinder, so that only the bulb (surrounded by a perforated steel cap) 

 projected below, and the scale (extending from 15° to 30° C.) above. 

 Tallow was poured round the wooden cylinder, and the whole thermo- 

 meter was then thrust into a bore-hole a metre deep, so that only the 



* ' Studien iiber die Warmevertheilung im Gotthard,' i. Theil. ' Der Schwei- 

 zerischen Naturforschenden Gesellschaft zu ihrer sechzigsten Jahresversammlung 

 in Bex gewidmet,' von F. M. Stapff. Bern, 1877. 



