SCIENCE. 



375 



weights are 7^ and y/ 2 pounds, but the weights can be 

 varied to suit the resistance and the pressure by changing 

 the shot. Since these changes the performance ot the 

 clock has been tolerably good. Still this clock needs 

 much care, and being dependent on an unsteady pres- 

 sure of water a delay in the observations sometimes oc- 

 curs. The great length of the telescope, which exposes 

 it to the action of the wind, is also a hindrance to the 

 steady driving of the clock. 



The difficulty in turning the dome, of about 42 feet di- 

 ameter, has increased. This difficulty is caused proba- 

 bly by the uneven settling of the supporting walls, and 

 the bulging of the dome in the direction of the slit. The 

 labor of turning the dome through a revolution is so 

 great that lists of north and south objects are prepared 

 beforehand by the observer in order to avoid as much as 

 possible the turning of the dome. 



After some practice, and on becoming familiar with 

 the instrument and micrometer, my manner of observing 

 a double star has been as follows : In order to measure 

 the angle of position the two wires are separated a con- 

 venient distance and the stars are placed between them. 

 The position-circle is turned by the hand until both stars 

 appear midway between the wires, and then the circle is 

 read. The light having been taken out of the microm- 

 eter, the wires are turned thirty or forty degrees forward 

 and backward several times before the light is thrown 

 on the wires again for the purpose of making the settings 

 of the circle as independent as possible, and another 

 reading is made. Generally four readings of the position- 

 circle are taken. Then this circle is turned 90 from the 

 mean of the readings and the double distance is meas- 

 ured. First the stars are bisected by the wires and the 

 micrometer is read ; then the wires are reversed and the 

 stars are bisected again. The wires are then restored to 

 their original position and another double distance is 

 measured. Two such distances are generally observed. 

 An estimated value of the angle of position is always re- 

 corded, as well as the sidereal time of trie observation, 

 and also an estimate of the weight of the observation. 

 This weight depends simply on the condition of the 

 images of the stars, and the numbers 1 to 5 are used for 

 expressing the weights ; 1 denoting a very poor condition 

 of the images, 3 an average condition, and 5 a perfect 

 condition. I have very rarely observed double stars 

 when the images were so poor as to be given the weight 

 1. As far as possible I have avoided all knowledge of 

 the angles and distances observed by other astronomers. 

 In my observing-list these quantities are omitted, and no 

 comparison with other observations is made until my own 

 observations of a star are completed. It is possible, there- 

 fore, that in some cases my angles may differ by a mul- 

 tiple of a quadrant from those observed elsewhere. 



I have omitted observations of color and of magnitude. 

 These observations have now become a specialty, and 

 such observations as I could make would not do much 

 more perhaps than tend to introduce confusion. In the 

 case of stars observed by the Struves, to which most of 

 my observations belong, I have adopted their magni- 

 tudes. In most cases these magnitudes are brighter than 

 those of the scale to which I have been accustomed ; 

 thus what the Struves would call a 7th or 8th magnitude 

 I would call an 8th or a 9th. 



Very few of the observations have been made in the 

 twilight, which offers the best conditions for observing 

 double stars, since, the observer residing at a distance 

 from the observatory, it has not been convenient to do 

 this. 



With such a large objective great changes occur in the 

 appearance of the stars during a single night. Generally 

 so long as rapid changes of temperature are going on 

 the performance of the object-glass is not good. But on 

 a few nights of the year, when all the atmospheric con- 

 ditions are favorable, the performance of the glass is ex- 

 cellent, and its separating power is all that could be de- ' 



sired. Usually ruddy and reddish stars are the most 

 difficult to observe, a result which may be caused by the 

 figure of the objective. After having been in use two 

 years the form of the lenses seemed to have undergone a 

 slight change, and in the beginning of May, 1876, the 

 surfaces of the flint lens were refigured by Mr. Alvan 

 Clark and his son, Mr. Alvan G. Clark. This is the 

 only change that has been made in the objective. On 

 ? single occasion water collected between the lenses, and 

 they were taken out, cleaned by Mr. Gardner, and re- 

 turned to their cell with very little trouble. 



Until March, 1878, all the observations were made 

 with my left eye; but having used my eyes very much 

 during the preceding year, and having done a good deal 

 of computing by gaslight, my eyes became weakened. In 

 March, 1878, while observing the stars in the Trapezium 

 of Orion with a field illumination which was very un- 

 steady, my left eye suddenly became bloodshot. After a 

 rest of a week the eye resumed its natural appearance, 

 but on observing again the blood reappeared in the eye. 

 I then began to use my right eye, and have used it since 

 in most of the observations. From a number of trials I 

 think that this change of eyes has produced only a small 

 change in my habit of observing an angle of position. 

 Still it is possible that some systematic difference in the 

 angles may exist on account of this change, as there was 

 at first some awkwardness in observing with my right 

 eye. In all my observations the head of the observer 

 was kept in an upright or natural position." 



The elaborate introduction of Professor Hall leaves us 

 little scope for further explanation. We may state, how- 

 ever, that the tables in which these observations are con- 

 densed cover nearly 150 folio pages, and will be accepted 

 as a valuable addition to the literature of this subject, 

 which has been much developed of late by the researches 

 of Mr. Burnham and others. 



A PARASITE IN /EGERIA SYRINGE. HARR. 

 By G. H. French, Carbondale, 111. 



When examining the stems of some lilac bushes in 

 my yard, I found a place in the bark of one where it 

 seemed that an /Egerian pupa might soon protrude 

 for the purpose of liberating the moth. Upon cutting 

 away the thin film of bark, I found the end of a 

 chrysalis visible. I carefully cut away the wood, took 

 this out and put it in a jelly dish surrounded with lilac 

 leaves to prevent its drying up, and waited for the imago 

 to come forth. June 5th, a week after the chrysalis had 

 been put into the jelly dish, I saw something among the 

 leaves which I supposed was the expected moth, but 

 which proved to be a hymenopter. I did not know but 

 the insect might be one of the boring bees that often 

 resort to the holes left by /Egerians in which to rear their 

 young, but an examination of both the insect and the 

 empty pupa case assured me that I had a parasite. The 

 chrysalis was certainly that of an /Egerian, having all the 

 characteristic marks of the pupae of that family ; and the 

 insect in emerging from it had gnawed a hole near the 

 end on the left side instead of the usual method of emer- 

 gence of insects from their own pupa cases. More than 

 this, the specimen was a true Ichneumonide and not a 

 Crabronide as I at first thought it might be. This is the 

 first time I have known of any parasite working in the 

 ^Egerians. 



I make the parasite to b'; Phccogenes Aler, Cres. It is 

 shining jet black, 40 of ^n inch long, the antennas 25 

 jointed, the first 8 black, the next 4 white and the rest 

 dark brown. The joints of the legs are a little pale. 



It is impossible for me to say when the parasite was 

 introduced into its host ; but it must have been before it 

 pupated, because the chrysalis when taken from the bush 

 was entire, showing no broken place. That the /Egerian 

 was sE. Syringce, I have no doubt, 1 do not know of any 

 other boring in the lilac. — Papilio. 



