ON THE CALCULATION OF SDN-IIEAT COEFFICIENTS. 89 



over a considerable length of time, and carried on in places specially 

 adapted for the purpose. 



For we know that meteoric dust does fall, and further observations 

 onght, if possible, to be directed rather towards an approximate estimate 

 of the quantity which falls within a given time. Difficulties very likely 

 will be found in the determination of the locality in which the observa- 

 tions should be conducted. The place ought to be sheltered as much as 

 possible against any ordinary dust not of meteoric origin. The lonely 

 spots best fitted for these observations ai-e generally accessible to occa- 

 sional experiments only, and do not lend themselves easily to a regular 

 series of observations. Nevertheless, experiments continued for a few 

 months at some elevated spot in the Alps might lead to valuable results. 



The Committee would like to draw attention to an instrument which 

 might be well fitted for snch observations. It was devised by Dr. 

 Pierre Miquel for the purpose of examining, not the meteoric particles, 

 but organic and organised matters floating about in the air. A descrip- 

 tion, with illustrations, will be found in the ' Annuaire de Montsouris ' for 

 1879. 



Two forms of the instrument are given. In the first form, which is 

 only adapted to permanent places of observation, an aspirator draws a 

 quantity of air which can be measured through a fine hole. The air 

 impinges on a plate coated with glycerine, which retains all solid matter. 

 By means of this instrument we may determine the quantity of solid 

 particles within a given volume of air. 



The second more portable form does not allow such an accurate 

 quantitative analysis. The instrument is attached to a weathercock, and 

 thus is always directed against the wind, which traverses it, and 

 deposits, as in the other permanent form, its solid matter on a glycerine 

 plate. An anemometer placed in the vicinity serves to give an approxi- 

 mate idea of the quantity of air which has passed through the apparatus. 

 These instruments have been called aeroscopes by their inventor. 



But perhaps the simpler plan of exposing a large horizontal surface 

 covered with glycerine, and examining the dust deposited on it, will 

 prove the most efficient for the purpose which the Committee has in 

 view. 



Second Report of the Committee, consisting of the Kev. Samuel 

 Haughto\, M.D., F.R.S., and Benjamin Williamson, F.R.S., ap- 

 pointed for the Galcnlation of Sun-heat Coefficients. Drawn 

 up by Dr. Haughton. 



The Committee placed upon the table the volume of calculations relative 

 to the equator, as a specimen of the five volumes which will ultimately 

 be placed, for reference, in the library of Trinity College, Dublin ; and 

 explained the method by which the reductions had been made. 



The formulae, by means of which the calculations were made, have 

 been published in the British Association Report for the Sheffield meeting 

 (1879), and the Royal Irish Academy have undertaken the publication of 

 all the summarised results in detail, so that it will not be necessary to ask 

 the Association to undergo the expense of printing them. 



