previous简单

Because flammable material couldn’t build up on the landscape, blazes tended to move slowly and peter out when they reached the footprints of previous burns.

由于易燃物无法在地面上大量堆积，火势往往蔓延缓慢，并在到达以往过火区域时逐渐熄灭。

the causes of previous burns.

以往火灾的起因。

A butterfly takes off so quickly it is still impossible to react quickly enough to capture that take-off but if he half-presses the shutter, the camera saves the 70 previous frames before the moment he actually takes the picture.

蝴蝶起飞得太快，人仍然不可能反应快到捕捉到起飞的那一刻，但如果他半按快门，相机就会保存他真正按下快门之前的70帧画面。

Researchers analysed the frequency and impact of gaps greater than 2 seconds during conversations, including an overview of previous studies which indicate that the fear of awkward silences can be so extreme that people avoid talking to strangers, even though doing so is likely to be an enjoyable experience.

研究人员分析了谈话中超过2秒的停顿出现的频率及其影响，其中包括对以往研究的综述，这些研究表明，人们对尴尬沉默的恐惧可能极其强烈，以至于会避免与陌生人交谈，尽管与陌生人交谈很可能是一种愉快的经历。

One previous study looked at the Efé people of the Democratic Republic of Congo.

此前的一项研究考察了刚果民主共和国的埃菲人。

Throughout the trip, Jackson juggled multiple cameras and plate sizes using the “collodion process” that required him to coat the plates with a chemical mixture, then expose them and develop the resulting images with a portable darkroom. The crude technique required educated guesses on exposure times, and involved heavy, awkward equipment — several men had to assist in its transportation. Despite these challenges, Jackson captured dozens of striking photos, ranging from majestic images like his now-famous snapshot of Old Faithful, to casual portraits of expedition members at the camp. While veterans of previous expeditions wrote at length about stunning trail sights, these vivid photographs were another thing entirely.

在整个旅途中，杰克逊使用“火棉胶工艺”同时摆弄多台相机和多种尺寸的底片，这种工艺要求他先给底片涂上一层化学混合物，然后曝光，再用便携式暗室冲洗出影像。这种简陋的技术需要凭经验推测曝光时间，而且所用设备笨重难使——需要好几个人协助搬运。尽管困难重重，杰克逊还是拍下了几十张引人注目的照片，从他那张如今已闻名于世的老忠实泉快照这样的壮丽画面，到营地里考察队员的随意肖像，不一而足。以往考察的老手们曾长篇累牍地描写沿途的壮丽景色，而这些生动的照片则完全是另一回事。