452 Proftssor Tyndall [May 3, 10, and 17, 



sometimes adopts means to this end which defeat themselves. Such is 

 the case when he dwells with reiteration on the refined and exquisite 

 pleasure which he derives from being of service to humanity. Some 

 also would deem him tedious, though I deem him courageous, when 

 he deals with the details of his schemes. He leaves no stone unturned 

 in his effort to render himself clear. He is in many cases simply 

 writing out a specification, to be followed in all particulars. He 

 gives directions as to the manner in which a slice of hasty pudding 

 is to be eaten. A small pit is to be dug in the centre of the cake, a 

 piece of butter placed in tlie pit, while the removed bit is to be placed 

 on the butter to aid in molting it. You then begin at the circumference 

 of your pudding, and eat all round, dipping each piece in the butter 

 before conveying it to the mouth. Such details were sure to provoke 

 sarcasm, and they did provoke it. But amid the verbosity we have 

 incessant flashes of practical wisdom and examples of intellectual 

 force. Wlien he ceases to tliiid^ of the exquisite delight of his phi- 

 lanthropic labours — ceases to think of himself — and permits his own 

 personality to be cifaccd by his subject, we see Eumford at his best; 

 and his best was excellent. Suggestion follows suggestion, experi- 

 ment succeeds experiment, until he has finally exhausted his subject, 

 or is pulled up by inability to proceed further. 



He tested quantitatively the relative intensities of various lights, 

 constructing, while doing so, his well-known photometer. Placing 

 two lights in front of a white screen, and at the same distance from it, 

 and fixing an oj^aque rod between the lights and the screen, he obtained 

 two shadows corresponding to the two lights. When the lights were 

 equally intense, the shadows were equally dark, but when one of the 

 lights was more powerful than the other the shadow corresponding to 

 that other was rendered pale, br cause the light from the most intense 

 source fell upon it. Removing the more intense light further from 

 the screen, until a point was reached when the shadows appeared 

 equal, Eumford obtained all the elements necessary for the computa- 

 tion of the relative intensities of the lights. He had only to apply 

 the law of inverse square, which makes a double distance correspond 

 to a fourfold intensity, a treble distance to a ninef(dd intensity, and 

 so on. In connection with these experiments he dwells repeatedly 

 upon a defect which harasses the official gas examiners of the present 

 day, and that is the fluctuations of the candles used as standards of 

 measurement. These photometric measurements are succeeded by a 

 brief, but beautiful essay on " Coloured Shadows," which, in connec- 

 tion with another short essay on the " Harmony of Colours," strik- 

 ingly illustrates Rumford's penetration and experimental skill. He 

 produced two shadows, one from daylight, the other from candle- 

 light. The daylight shadow being shone upon by the candle, was, 

 as might be expected, yellow, because the candle sheds a yellow light. 

 But the other shadow, instead of being colourless, was " the most 

 beautiful blue that it was possible to imagine." He states clearly 

 that the colour of one shadow is real, while that of the other is imagi- 



