Hmm, that could be it though I'm still doubtful. Thawne tried to use a tachyon device to get back to the future.

Thawne was having issues reaching the speed he needed to time travel (The chair was acting as a recharging device for his speed).  A speedster needs to vibrate there body at a specific frequency as well to cross dimensions (that is how they do it in the comics I don't know if the TV show will use this but they have confirmed in the series that each earth vibrates at a different frequency but exists in the same space as all other earths, so for a speedster to travel to another dimension they need to alter there bodies vibration-al frequency to match the earth they want to travel too)

That Wraith in the last episode (17) was one hell of a creepy thing.

Can't wait for

But...but...White Canary!!

Jonah Hex in next week's Legends of Tomorrow

With Melissa Benoist as Power Girl?

Google's image search reveals that Power Girl should be extremely "appealing". I hope they don't bring down her charm by choosing the wrong actress like in Batman vs Superman.

Probably, based on what they are saying.  However it would make more sense to get an actress who looks similar to Melissa but has a different physique since Power Girl is normally physically different from Super Girl despite being the same person technically (she is normally taller, broader in the shoulders and bigger in fan service areas) plus Power Girl is a little older than Super Girl (4 - 5 years though in the comics Super Girl is a teen).

Plus it would be a better idea to have different actresses since The Flash shoots in Vancouver and Super Girl shoots in California (or where ever it shoots)