for more, i spoke a short time ago with "new york times" cairo bureau chief declan walsh.lan walsh, thank you for joining us. this seems to have been an unusually ruthless attack. they kept on shooting as the ambulances arrived? >> absolutely, that's right. there were -- the gunmen arrived in several vehicles. they split up into teams. some of the gunmen went inside the mosque. they started shooting the worshipers immediately after a bomb had gone off. other gunmen waited outside and shot people as they tried to flee. >> woodruff: and it was unusual that, in the past, they have been going typically after christians. this time, it was at a mosque. >> that's right. this is extremely unusual. this attack the extremely unusual both by the size of the attack, the number of people who have been killed. this is the largest attack in modern egyptian history, and it's also, as you say, the target. over the last year the islamic state have carried out attacks on coptic christian churches in egypt but not a muslim mosque. we do not have a claim of responsibility for this attack but i

a shipping container on board i do has a good effect your the big read the book is out here today declan and thanks very much why did the stuff pass of him why he's so interested there was so actually in particular we're interested in the tiny particles that are in the air we call them aerosol aerosol particular and they have very important for the water cycle and because they form clouds without these tiny particles we would not have any clouds in our atmosphere so it would never rain. earth would be a completely different planet to see if the hot ticket spent ten full droplets on not that we use this machine and then a cloud machine here that you know we should make here are some are making our own cloud in here so it's very important floss to understand politics clouds formed before the industrial revolution before humankind actually started burning fossil fuels in large amounts. because it makes a big difference for our climate for the clouds and for the hydrological cycle in general. climate change models a generally better at predicting variations in temperature rather than precipi