Proceedings. 117 



due merely to the bending of the needle by its own weight. 

 The Greenwich records, however, still give the various 

 readings of needles of three different lengths, and it is an 

 axiom in observatories that long needles give a bigger dip 

 than short ones, no one outside Manchester apparently 

 being aware of Dr. Joule's explanation. 



Dr. HODGKINSON exhibited a specimen of iridescent 

 chlorate of potash mounted in a special way in order to 

 demonstrate that the colour is produced, not by the inter- 

 ference of one thin plate, but by numerous thin plates. The 

 thin plates were readily seen in the specimen by means of a 

 hand magnifier, and the exhibit confirmed a prediction 

 made several months since by Lord Rayleigh. 



Mr. Faraday adversely criticised the latest Blue-book 

 issued by the Solar Physics Committee. He called atten- 

 tion to the absence and confusion of dates and signatures, 

 the imperfection of the references, and the want of con- 

 tinuity with the previous report. The Committee had 

 been in existence since 1879, and it had only issued two 

 reports. The first had been compiled seven years pre- 

 viously, and the second had just appeared. Mr. Faraday 

 complained that the spectroscopic work described did not 

 appear to be the work which the Committee was appointed 

 to carry on, and that the report did not present the results 

 which the practical reader hoped to find in it. A discussion 

 on the desirableness of the abolition of the Committee, in 

 which Mr. H. H. Howorth, M.P., took part, ensued. 



Professor Dixon read a paper on the combination of 

 hydrogen and chlorine alone and in the presence of other 

 gases. An apparatus was exhibited whereby the gases can 

 be measured and exploded without coming in contact with 

 any liquid. A protracted discussion ensued, in which Dr. 

 Schunck, Dr. Bottomley, Mr. Francis Jones, Professor 

 Schuster, and others, took part. 



