420 Mr. W. R. Birt un the Hail Storm of May 5, 1850, 



blished in a direction contrary to its primitive one when the 

 element of copper and iron is heated in the flame of a spirit 

 lamp*. 



I have likewise on several occasions made experiments on 

 thermo-electric currents by interposing variable resistances in 

 the circuit, so as to maintain the needle of the galvanometer 

 at a constant deflexion for the different temperatures commu- 

 nicated to the solderings. For that purpose, I employed 

 sometimes Prof. Wheatstone's rheostat, sometimes a simple 

 metallic wire strung by a weight, and of which I inserted dif- 

 ferent lengths in the circuit ; but I thus obtained much more 

 variable and uncertain results than by the method above de- 

 scribed. I added in this manner to anomalies produced by 

 the thermo-electric elements themselves those due to the irre- 

 gularities of the conductibility of the resisting wires, which 

 will always render this method very uncertain for the study 

 of feeble electric currents. 



To conclude, if the numerous experiments which I have 

 made on the thermo-electric currents do not demonstrate that 

 these currents cannot in future be employed for the measure- 

 ment of temperatures, they at least show that we are still far 

 from being acquainted with all the circumstances which exert 

 influence on the phaenomenon, and of being able to establish 

 the conditions in which the thermo-electric elements ought to 

 be placed so that the intensities of the currents may depend 

 solely on the temperature. 



LIII. On the Hail Storm of May 5, 1850, as observed at the 

 Kew Observatory. By Mr. W. R. BiRTf. 



To Richard Taylor^ Esq. 



Kew Observatory, Old Deer Park, 

 My dear Sir, Richmond, Surrey, May 14,1850. 



BY permission of the Committee of the Kew Observatory 

 of the British Association for the Advancement of Science, 

 I annex a record of observations made at Kew on the Hail 

 Storm of May 5, 1850, and beg to add my views of the phae- 

 nomena. 



" At half-past 5 in the afternoon, on May 5, 1850, my atten- 

 tion was arrested by a very heavy and dark collection of clouds 

 {cumuli) in the N.E., from which rain was falling in the di- 

 stance. The appearance of the clouds was very black and 

 threatening. Below this black collection, which occupied a 



* Ann. de Chim. et de Phys., vol. xxxi. p. 385. 

 t Communicated by the Author. 



