Natural History. 185 



time. If the colour entirely disappears, add instantly from 

 the measure D, until the colour becomes slightly green; the 

 quantity of test-liquor then deficient in the measure, will indicate 

 the strength of the chloride, provided the second portion added 

 was not more than ^^y of a degree. If it amounts to more, a second 

 operation must be performed : the measure is again to be filled 

 with test-liquor, and then as much poured from it into the tumbler 

 as was found requisite by the last operation, and a hundredth or 

 two over, and then proceed as before. When the quantity pro- 

 duces, at once, the proper tint, an expression is given by that 

 quantity, of the strength of the chloride, correct to at least 3^ part. 

 The tube E is intended to make the trial by pouring the indigo 

 suddenly into the chloride. The quantities are ascertained as be 

 fore, and then the trial is repeated by measuring out the proper 

 quantity of test-liquor into the tube E, and pouring it rapidly into a 

 new measure of chlorine ; test-liquor is then to be added, until the 

 green tint is obtained just as before. The trials made in this way, are 

 to be conducted exactly as in the former manner, but as the results 

 are the same, it has nothing to render it preferable. — Ann, de 

 Chi?n. xxvi. 162. 



Gramme 15.44 grains. 



Kiiogramme 21b. 3oz. 5dr. 



Litre 2.1133 pints. 



III. Natural History, 8j-c. 



1. Aurora Borealis in Iceland. — Dr. Thienemann, who passed 

 the winter of 1820-21 in Iceland, made numerous observations 

 on the Aurora Borealis, of which the following are the general 

 results: — 1. The Aurora Borealis has its place in the lightest 

 and highest clouds of our atmosphere. 2. It does not occur in 

 the winter and at night-time only ; but at all times, being visible, 

 however, only in the absence of the sun's rays. 3. It has no de- 

 terminate relation with the earth. 4. No sound occasioned by it 

 has ever been heard. 5. The form in Iceland is generally that of 

 an arc, extending from N.E. to W.S.W. 6. The motions are va- 

 riable, but always occurring within the limits of the clouds contain- 

 ing the meteor. — Revue Ewcj/.xxii. 734. 



2. Drosometer. Annual quantity of Dew. — M. Flaugcrgues has 

 been engaged at Viviers (Ardeche) in endeavouring to estimate 

 the quantity of dew deposited at various times in the course of 

 a year. The instrument contrived for this purpose was a 

 circular tin plate 109 lines in diameter, with a border two lines ia 

 height ; it was painted with oil-paint of a grey colour, and sup- 

 ported on a stick in the midst of a garden, about three feet six 



