No. 2.] BRITISH ASSOCIATION MEETING. 133 



parably superior in miuuteness and accuracy of delineation to 

 anything ever attempted previously. These maps now constitute 

 the standards of reference for all workers in the field. Pliicker 

 and Hittorf opened ground in advancing the physics of spectrum 

 analysis, and made the important discovery of changes in the 

 spectra of ignited gases produced by changes in the physical 

 condition of the 2;as. The scientific value of the meetin<2;s 

 of the British Association is well illustrated by the fact that 

 it was throuo'h conversation with Pliicker at the Newcastle meet- 

 ing that Lockyer was first led into the investigation of the effects 

 of varied pressure on the quality of the light emitted by glowing- 

 gas which he and Frankland have prosecuted with such admirable 

 success. Scientific wealth tends to accumulation accordins: to the 

 law of compound interest. Every addition to knowledge of pro- 

 perties of matter supplies the naturalist with new instrumental 

 means for discovering and interpreting phenomena of nature, 

 which in their turn afford foundations for fresh generalizations, 

 bringing gains of permanent value into the great storehouse of 

 philosophy. Thus Frankland, led, from observing the want of 

 brightness of a candle burning in a tent on the summit of 

 Mont Blanc to scrutinize Davy's theory of flame, discovered that 

 brightness without incandescent solid particles is given to a purely 

 gaseous flame by augmented pressure, and that a dense ignited 

 gas gives a spectrum comparable with that of the light from an 

 incandescent solid or liquid. Lockyer joined him ; and the two 

 found that every incandescent substance gives a continuous spec- 

 trum — that an incandescent gas under varied pressure gives bright 

 bars across the continuous spectrum, some of which, from the sharp, 

 hard and fast lines observed where the gas is in a state of extreme 

 attenuation, broaden out on each side into nebulous bands as the 

 density is increased, and are ultimately lost in the continuous 

 spectrum when the condensation is pushed on till the gas becomes 

 a fluid no longer to be called gaseous. More recently they have 

 examined the influence of temperature, and have obtained results 

 which seem to show that a highly attenuated gas, which at a high 

 temperature gives several bright lines, gives a smaller and smaller 

 number of lines, of sufiicient brightness to be visible, when the 

 temperature is lowered, the density being kept unchanged. I 

 cannot refrain here from remarking how admirably this beautiful 

 investigation harmonizes with Andrew's great discovery of contin- 

 uity between the gaseous and liquid states. Such things make 



