534 Ml'. J. Newman on a new Evaporatiny Gauge. 



manner essentially different from the colours of the spectrum 

 when the latter are weakened by the addition of white light. 



In conclusion I give the following small table ; it furnishes 

 a general view of the combinations of every two colours, and in 

 its construction five colours are assumed, by the union of which 

 the colours of the spectrum are represented with sufficient 

 accuracy. In the first horizontal and the first vertical series 

 stand tlie simple colours; the compound colours which follow 

 from their union are found at the intersection of the correspond- 

 ing horizontal and vertical columns. 



LXXXII. Description of a new Evaporutiny Gauge. 

 By Mr. John Newman. 



To the Editors uf the Philosophical Mayazine and Journal. 



Gentlemen, 



I HAVE for many years noticed that the meteorological jour- 

 nals kept by scientific observers omit all mention of the 

 quantity of w^ater evaporated from the earth's surface. This 

 omission has, I believe, arisen from the want of a correct instru- 

 ment, or one sufficiently delicate in its indications. 



After much consideration, I beg to hand you for insertion in 

 your Journal, the description of an instrument which I believe 

 will be found efficient, adding to the completeness and useful- 

 ness of the meteorological notices of those who arc pleased to 

 use it. 



It consists, as you will observe (from the accompanying sketch), 

 of a short cylinder 12 inches in diameter, having connected with 

 it, by means of a stopcock, a glass tube graduated to hun- 

 dredths, aud tcrujinating in a lower vessel, which will con- 



