12 



Tribune Extras Lecture and Letter Scries. 



Prof. Henry said that we are inviting thousands 

 of foreigners to come here, and we ought to be able 

 to tell them what we have to offer them. For this 

 purpose a survey of the whole United States ought 

 to be made. We have three organizations for this 

 purpose the Coast Survey, the Engineers' Survey, 

 and this Civilians' Survey. It is very desirable that 

 there should lie no wrangling between these organi- 

 zations; that their work be brought into coordina- 

 tion and unity. lie recommended that the Academy 

 take this matter into consider:) lion, and perhaps 

 suggest the I'ormati >n of a commission. 



Prof . J. Lawrence Smith of Louisville, Kentucky, 

 followed up this observation with one on the lack of 

 unity in the State surveys. His own State suffered 

 much from the need of correct surveys from fixed 

 points determined by the Coast Survey. It is ex- 

 ceedingly desirable that the method and system of 

 all surveys be placed under otiehead and conducted 

 with uniformity. 



Col. Forshey of Louisiana enforced the foregoing 

 views by hi.s experience in that State and remarked 

 also on the value and interest of Prof. Hoyden's 

 work. In the matter of hydrographi" surveys there 

 was almost an equal deficiency of unity of plan and 

 useful results. 



Gen. Barnard 01 Washington referred to the ex- 

 treme difficulty that was found in conducting the 

 operations of the war without maps of a topograph- 

 ical character. He considered that much of the 

 delay which characterized our undertakings in the 

 war \v;is principally due to our ignorance of the 

 country where they were carried on an ignorance 

 of topographical details paralleled in no European 

 countfj'. 



He also alluded to the difficulties which ordinary 

 civil engineering operations find in our deficient 

 surveys. The opening of a water supply, for in- 

 stance, when; a canal or railroad was being con- 

 structed, could not bo predicated with any certainty 

 when the geological and topographical features of a 

 section of country were almost unknown. 



Col. Forshey was glad to hear the proposition 

 (suggested by Prof. Henry) that a Commission be 

 appointed to unify the surveys throughout the 

 United States. 



Prof. Henry mentioned, in the absence of Dr. 

 Bessel, that the entire scientific operations of the 

 Polaris were under his management, and that his 

 report of the work effected during the voyage of 

 that vessel would be presented to the Academy, in 

 accordance with the provisions of the acts of Con- 

 gress concerning that expedition. 



MiNERALOGICAL NOTES. 



BY PKOK. 15. KII.LIMAy OF NEW-HAVEN. 



The, subject which he proposed to treat was 



the telluric ores of Colorado. The rock-s are principally 

 pnetssic, and frraoite \vitii excess of feldspar or quartz. 

 At tbe place where tlie miner. il i found there is a re- 

 luurkablu dyke of ~>0 feet in thickness. It is on the Mile 

 Of this dyke that the mineral roiitaiiiini; tho httlc-knosvn 

 substance tellurium is found. Prof. Silliman snowed 

 the evidence that tlie tellurium was introduced by tho 



Plutonic invasion of this dykp. He had found in many 

 instances that telluric ores were associated with 

 cold, and the association was very unfortunate 

 for the gold miner, as in one iustancb 

 $3,010 worth of gold thus associated was thrown uway 

 (through ignorance), while the yield of tho rest of the 

 ore was only $10 or $50 10 the ton. Prof. Sillimau asked 

 Prof. End hch to perform an experiment, showing the 

 presence of tellurium by using concentrated sulphuric 

 acid. A bright purple color was rapidly obtained when 

 the ore was thus treated with heat, in a test tube. In 

 one specimeu of these telluric ores there was 55,000 

 extracted from a ton. Specimen-! of telluric ores were 

 exhibited, and Prof. Sillunau mentioned that thesn and 

 many other very valuable specimens, now the property 

 of the Smithsonian Institution, were procured in Prof. 

 Haydeu's surveys. 



ON THE LAWS OF CYCLONES. 



BY PROF. WILLIAM FERREL OF THE COAST SURVEY. 



There were at one time two rival theories 

 with regard to the motions of the atmosphere in cyclones. 

 According to E spy's theory, called the radial theory, 

 the atmosphere flowed iu from all sides toward the 

 center in the direction of the radius, and i.sceiided in 

 the middle of the cyclone and flowed out above. Ac- 

 cording tojRedfield, Reid, and others, the motion of the 

 atmosphere above aud below was that of a circular 

 gyration around the center of the cyclone, and there 

 was no motion either to or from the center. 



In the. year 1859 in a paper published in Kunkle's 

 Mathcmalhical Monthly, Prof. Ferrel first demon- 

 strated the effect of tho earth's rotation upon 

 auy body moving upon its surface, which was to 

 cause a deflecting force at right angles to the di- 

 rection of motion, to the right hand in the northern 

 hemisphere, but to the left iu the southern. It was also 

 shown that tho off 'ct of this deflecting force upon air 

 tending from all sides toward a center, was to cause it 

 also to gyrate around this center, aud that 

 consequently Espy's theory could not be true. 

 If the atmosphere has a circular gvration, 

 the deflecting force arising from tho earth's rotation is 

 in the direction of the radius from the center, and 

 causes a depression and low barometer in tho center; 

 hut there is no force to overcome the resistance to the 

 gyration, aud hence the atmosphere is soon brought to a 

 state of rest. Taero must, therefore, in all cases be 

 some motion below, toward tho center of the 

 cyclone, so that tho deflecting fore:' depending 

 upon tho earth's rotation arising from tins com- 

 ponent of the motion, may overcome tho resistance 

 to gyrations; else tin; gyration KOOH ceases. 

 The resultant of the gyratory motion and 

 the motion toward tho center gives a motion, the 

 direction of which makes an anglo with tho iso- 

 bar, or lino of equal barometric pressure. (Here Prof. 

 Ferrel drew a circle on the blackboard, show-in;,' the line 

 of tin- isobar in:; perfect cyclone.) The greater the re- 

 sistances, the greater this angle inns' be, and hence, 

 since resistance Is as the square to tile velocity, all other 

 things beiii;; I be same, the mororapi.l tho motions of tho 

 almnspliere.il] the cyclone, tlio greater must be t his an- 

 gle. (Tho unglo was shown on the blackboard as formed 

 by a tangent to tho circular isobar.) 



On tho open sea. where, the amount of resistance i8 

 small, especially wiicn tho velocities are not very great, 

 this angle must be small, nnd the gyrations nearly cir- 

 cular, as RednVld's theory requires. In violent tornadoes 

 on laud, where the resistances are very great, this 



