Different kinds of Coal for the purpose of Illumination. 273 



might lead ; and having once begun with it, I thought it 

 better to complete the experiments with it. 



Since these experiments were finished, I have performed 

 others, to enable me to find the best jet for the purpose now 

 recommended. I had accordingly jets made with accuracy, 

 the apertures in which were the 25th, 30th, 35th, 40th, 45th, 

 and 50th of an inch ; with all of which numerous trials were 

 performed, to ascertain the consumpt and pressure. I soon, 

 however, rejected the first two, because they gave an unsteady 

 flame ; while the pressure-column in the gauge was not of 

 any great length. With the remainder, the flame was more 

 steady, and more easily measured, while the pressure-column 

 was of sufficient length to be easily marked. I soon, however, 

 also rejected the burner, No. 50, because imless the pressure 

 on the street-pipes is great, it does not give a flame of suf- 

 ficient height ; indeed the same is sometimes the case with jet 

 45. For these reasons, I now prefer the jet 40, because, 

 while it gives a very steady flame at 5 inches, the water- 

 column in the gauge is much longer than when a jet 33 or 35 

 is used ; and thus, any slight inaccuracy, in noting the pres- 

 sure, leads to a smaller error in the results, than when the 

 same inaccuracy is committed, in noting the pressure when 

 the water-column is not so long. 



The following is the results of trials made with the diff"er- 

 ent jets I have mentioned : — 



Trials luith Flame. 



