138 PHILOSOPHICAL TRANSACTIONS. [aNNO J 757. 



and 6 pears to one of 5. The next morning the urine of both appeared of a very 

 lively red colour, as if tent wine had been mixed with clear water. The urine of 

 the eldest was deeper coloured, and of a darker look : the youngest (who always 

 naturally made clear urine) was of a more lively and beautiful red. Next day he 

 gave 6 pears to a negro wench, who gave suck, and strictly forbad her suckling 

 her child for 6 or 8 hours ; and then taking some of her milk in a tea-cup, and 

 setting it by for some hours, the cream had a reddish lustre, though it was very 

 faint. He was led to this last experiment by an observation, which he made on 

 the milk of cows, which had fed in an indigo-field : the indigo had not only 

 tinged their urine blue, but the cream of the milk was cf a most beautiful blue 

 colour, and had a radiated appearance from the centre (Is it not hence probable, 

 that the dye is the oily part of the plant ?). The milk underneath was clear and 

 white as usual. 



XXX FI I. Of an Extraordinary Shower of Black Dust that fell in the Island of 

 Zetland, Oct. 20, 1755.* By Sir Andrew Mitchell, of fVestshore, Bart. p. 297. 



From Orkney Sir A. was informed, that about the time of the earthquake at 

 Lisbon, Nov. 1, 1755, the tides were observed to be much higher than ordi- 

 nary. He received from Zetland a letter, dated 28th May, 1756, from Mr. 

 William Brown, master of the grammar-school at Scalloway in that country, a 

 sensible and observing man ; stating, on October 20, 1756, between the, hours 

 of 3 and 4 in the afternoon, the sky being very hazy, as it uses to be before a 

 storm of thunder and lightning, there fell a black dust over all the country. It 

 was very much like lamp-black, but smelt strongly of sulphur. People in the 

 fields had their faces, hands, and linen, blackened by it. It was followed by 

 rain. Some people assign the cause of it to some extraordinary eruption of 

 Hecla. And the same was confirmed afterwards by several other persons in Zet- 

 land. At the time, the wind was from the s.w. which does not seem to favour 

 the opinion that the dust proceeded from an eruption of mount Hecla, which 

 lies about n.w. from Zetland ; unless it may be supposed, that a north wind 

 happening just before had carried this dust to the southward, and the south-west 

 wind immediately following had brought it back to the northward. 



The distance from mount Hecla to 2^tland is between 500 and 600 miles. 



XXXVI II. Of some Thermometers for Particular Uses. By the Right Hon. 

 the Lord Charles Cavendish, V. P.R.S. p. 300. 



The thermometer, pi. 7> fig' 1? is designed for showing the greatest degree of 

 heat, which happens in any place during the absence of the observer. It con- 



* See vol. 10, p. 687* of these Abridgements. 



