October 9, 1914] 



SCIENCE 



61S 



normal again unless the environment had been 

 essentially changed. 



In the main, the effects of this eruption on 

 marine vegetation were temporary. The burial 

 of rock that had served for anchorage wiU no 

 doubt interfere permanently in some places 

 with algse in the littoral zone. It is possible 

 that this same cause may also lessen the pro- 

 duction of the two large kelps, NereocysUs 

 lueiheana and Alaria fistulosa, but the evi- 

 dence now at hand indicates that these kelps 

 are well on their way toward recovery. 



George B. Rigg 



State University of Washington 



EFFECT OF LIGHTNING ON A BEINFOBCED 

 CONCRETE AND STEEL DOME 



Owing to the increased use of reinforced 

 concrete for buildings I have thought that an 

 account of the effects of lightning on a metal 

 dome surmounting walls of this construction 

 may be of some general interest and of par- 

 ticular interest to astronomers. 



On the afternoon of January 2 last occurred 

 the heaviest thunderstorm in the immediate 

 vicinity of the observatory since I came to 

 Cordoba. The conditions were well marked — 

 the weather had been very hot and sultry for 

 several days, the barometer had been falling 

 steadily and was low. The center of the storm, 

 judging from the clouds and their motions, was 

 not over a mile south by southeast of the ob- 

 servatory. In an area between one and two 

 miles in diameter the clouds were very dark 

 and low and masses of dark scud moved about 

 underneath them. 



In nearly all the storms which I had seen 

 here previously the discharges were nearly all 

 between clouds. (Perhaps because most of 

 them occur at night?) In this storm nearly 

 all of the discharges were between the clouds 

 and earth. 



Very heavy single flashes of lightning began 

 about 2" 20" p.m. Cordoba time — apparently 

 under the blackest part of the clouds and not 

 over a half mile away. All of these which I 

 saw were discharges between the clouds and 

 earth, as also with only one exception, were all 

 which discharged within a half mile of the ob- 

 servatory. 



The direction of motion of this storm, as is 

 usually the case, was from south to north. 

 After some half dozen discharges close to the 

 south there was a heavy one to the northwest 

 about three hundred meters away — then 

 another to the northeast about the same dis- 

 tance. 



On account of this being a heavy storm and 

 apparently passing directly over us, I was in- 

 terested to see what the effect would be on our 

 two new reinforced concrete walls and steel 

 domes sheathed with galvanized iron, and was 

 outside among the central group of buildings 

 and not over 100 feet from the dome in ques- 

 tion, one of them in full sight. 



A minute or two after the flash to the north- 

 east, mentioned above, there was a general il- 

 lumination close by, followed almost instantly 

 by the ripping sound of a very close stroke. 

 The interval between the flash and the sound 

 was certainly not over Ai second. To me the 

 sound appeared to be made up of three or four 

 separate discharges blended into one — not con- 

 secutive. 



I was standing within a few feet of the ma- 

 chine shops in easy hearing of the noise of the 

 machinery. This noise stopped instantly after 

 the flash. The main fuse on the light circuit 

 had been blown twice before the flash, probably 

 by induced currents. It was also blown again 

 at the time of the flash. 



Mr. Mulvey was in the underground optical 

 shop at the time and thought there had been an 

 explosion in the shop. He saw a flash and im- 

 mediately afterward the lights went out. It 

 was later ascertained that one lamp had burned 

 out, which probably caused the flash which he 

 saw in the shop. No other damage was done 

 there. The circuits and machines were care- 

 fully examined but aside from the fuses being 

 blown at the pump motor, on the 220-volt alter- 

 nating current no sign of a spark was found. 



The power and light currents were cut off 

 until about 6 p.m., when it was found that 

 fuses had been blown on our lines (which were 

 special ones) just outside the step-down-sta- 

 tion, some 400 meters away. No other effects 

 of the storm were noticed in or near this sta- 

 tion. 



