GOOD SEEING. 195 



thus \ iolently (.listurl) and cluini the iiir aloiiii" all the path of (lie hcuin 

 from the coelostat to the .solar image. 



This first experiment g-ratifyino-ly reduced the "hoiling" and pro- 

 duced an incontestibh" stiller image than when still air was used. As 

 a further test, a series of artificial double stars was now jMovided, and 

 the concave mirror, acting both as collimator and objective, ])rought 

 the images to focus, where they were examined with an eyepiece. 

 With the stillest air obtainable the images were not siiar}). and only 

 the coarsest dou]>les were resolva])le. Then tho ))lower was stai'ted 

 and the definition inunediatidy ])ecame sharj). \ iolently stirring the 

 air in the tube, then, eliminates all or nearly all the "boiling" of the 

 stellar image which arises within the tu))e itself wlieii using ordinary 

 still air. This e\])erinient concerned the air within the horizontal 

 tube onl}'. 



1 have next taken uj) ihc solar image formed by the niirroi' in the 

 al)ove tube. This is clearly impro\ed hy the stirring. ] have also 

 wished to try a tube something' like a prolonged dew cap, l)ut which is 

 arranged to be inclined toward the sun. The air in both can be 

 stirred together, ))ut experiment has not yet gone far enough to 

 demonstrate whether it has. as is ho})ed. any superiority connnensu- 

 rate with the special nuH-hanical difficulties involved. 



1 am not prepared to give ({uantitative estimates, which J hope to 

 furnish later, but all observers to whom I have shown these early 

 results on the sun have agreed, that if th(» ■'boiling'" was not wholh' 

 cured, what remained was but a small fraction of tJiat obtained with 

 still air. 1 have not i-ompleted these experiments, which I am still 

 pursuing at the observatory, but they seem to me to give promise of 

 an improvement of universal interest to observers, which justified the 

 making of tliis eai'lv announcement. I had hoped to ha\e shown the 

 Academy some photogra})lis of the sun taken, first, in Ihe ordinary 

 way, and agaui. witls the churned air, but the condition both of the 

 sun and of the sky of late has prcNcnted my o])taining them. 1 can, 

 to my regret, only give here a photograph of the images of the artifi- 

 cial double stars as seen through ordinaiv conditions, as distinguished 

 from those here mentioned, of artiticial "good seeing.'' 



