426 C. PIAZZI SMYTH ON MICROMETRICAL MEASURES OF 



Of course this a delicate insinuation that I have been trusting to such 

 labels : if it is not also intended to indicate that he who fills his own tubes, as 

 the actual writer of that sentence for behoof of the Committee of fifteen had 

 done for himself, may take a very high place among the philosophers of the 

 land. While any one who falls short of that particular tubular operation by 

 the smallest item, no matter in what company, or under what system of 

 friendly or scientific co-operation with others, — instantly pitches headlong down 

 a social precipice, and may only bring up afterwards among glass-blowers. 



Now it is perfectly true that I did not either make or fill my own tubes ; 

 and there has never been any secret about it ; for I have from the first joyfully 

 proclaimed who did that for me; and did it at last so well, that I could 

 conscientiously recommend them elsewhere. 



For as to the persons concerned, I have been very fortunate in interesting 

 in this matter intellectually, several gentlemen of education, ability, and 

 experience in both chemistry, scientific instrumentation, and business, viz., 

 first, M. Salleron, and then his successor M. Demichel in Paris; next Mr 

 Louis P. Casella, and then Mr Charles P. Casella in London ; and finally I 

 believe I may add, to name one deficient to none in persevering enthusiasm to 

 conquer every chemical difficulty that arose in his path, though with little 

 leisure and less of laboratory appointments, Mr W. H. Sharp of Messrs Kemp 

 & Co. in this city. 



With one or other of these gentlemen I have been in nearly continued 

 correspondence for the last six years, discussing and trying experiments for the 

 quality of the glass, size and shape of the tubes, materials of the electrodes, 

 strength of sparks, arrangement and bore of capillary, as well as the methods 

 of preparing the several gases, purifying them when made, removing occluded 

 gases from the electrodes both before and during the filling, and then finally 

 sealing. Sealing too not a single tube only, but a series at several stated and 

 pre-determined steps of pressure. 



But did I even then trust to either the necessary labels of some kind put 

 on these tubes, or to the long descriptive letters also sent to me % 



Certainly not, after the first few days of experience. 



For my plan ever since then has invariably been, on receiving a batch of 

 fresh tubes from any maker, to put them one by one into a testing apparatus ; 

 find out there what is in them by their stronger lines compared with the 

 general literature of the subject, put my own labels on them, and perhaps send 

 | of the batch back to the maker for faults that had escaped him; and then 

 would begin a correspondence to try and find out where, either in the making 

 of the gas, or the steps of its purification, the fault originated, and how it 

 might be avoided in a new set. 



Again, even with tubes that have passed this examination, I have usually 



