18 REPORT OP THE SECRETARY. 



the nucleus, us published in '' Experiments with Ionized Air " (Smith- 

 sonian Contributions to KnoAv ledge, vol. xxix, 1901) and ir "Struc- 

 ture of the Nucleus," issued as part of the same volume in 1903. The 

 investigation was carried on with the aid of a grant from the Hodg- 

 kins fund. Doctor Barus describes the nucleus as a dust particle 

 small enough to float in the air but larger than the order of molec- 

 ular size, and shows that such a particle precipitates condensation in 

 an atmosphere saturated with water in its immediate vicinity. He 

 nses the term " nucleation " to denote the number of nuclei per cubic 

 centimeter regardless of their source — which may be from mechan- 

 ical, thermal, chemical, high potential, or radio-active processes — or 

 their special properties. By far the greater number are initially 

 ionized, or at least carry an electric charge, and where they occur in 

 thousands and millions of approximately uniform size they give 

 rise to condensational phenomena of transcendent beauty and im- 

 portance. 



The articles printed in the Miscellaneous Collections are, as the 

 name of the series would indicate, miscellaneous in character. The 

 past year has added 38 numbers to this series of papers, including 

 several relating to the bibliography of chemistry ; an exhaustive 

 catalogue of Diptera, or two-winged flies, showing the geographical 

 distribution of several species known to spread disease ; accounts of 

 explorations in Alaska and among the Canadian glaciers; some in- 

 teresting poi)ular papers by Doctor Gill on the sculpin, the tarpon, 

 the ladyfish. and the carp, and a lecture by Dr. Andrew D. White on 

 the diplomatic service of the United States, the first of the series of 

 lectures under the Hamilton bequest. 



The Contributions and Miscellaneous Collections just spoken of are 

 published at the expense of the Institution fund in editions of 1,500 

 coj^ies, and are intended solely for distribution to the large libraries 

 and institutions of learning throughout the world. 



The Annual Rej^ort, on the other hand, is published by a (Tovern- 

 ment appropriation in an edition of some 12,000, and is intended 

 for a more general distribution. Primarily, this volume is a report 

 to Congress on the operations of the Institution during the year, but 

 its popular interest lies largely in its General Appendix, contain- 

 ing a number of pajDers showing the recent progress of the Avorld's 

 scientific work. To the selection of appropriate papers for this Ap- 

 pendix I have given much ])ersonal attention for several years past. 



The manuscript of the work of the late Dr. G. Brown Goode, on 

 some contributions of America to the progress of science, which dur- 

 ing the past year has been worked over by Mr. Kenneth M. Goode, 

 editorial assistant, is now almost in its final shape, and will, I hope, 

 appear as a Smithsonian publication during the coming year. 



